Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" As a manuscript Semenova Maria Gennadievna HOMO-LIGAND AND HETERO-LIGAND COORDINATION COMPOUNDS OF COBALT(II) AND NICKEL(II) WITH MONOAMINE CARBOXYMETHYL COMPLEXES AND SATURATED DICARBOXY ACIDS –0.020 inorganic chemistry ABSTRACT of the dissertation for the degree of candidate of chemical sciences Kazan - 2011 Copyright OJSC "Central Design Bureau" BIBCOM " & LLC "Agency Book-Service" 2 The work was done in the State Educational Institution of Higher Professional Education "Udmurt State University" Supervisor: Doctor of Chemical Sciences, Professor Kornev Viktor Ivanovich Official opponents: Doctor of Chemical Sciences, Professor Valentin Konstantinovich Polovnyak Candidate of Chemical Sciences, Professor Valentin Vasilyevich Sentemov Leading organization: Kazan (Volga Region) State University 212.080.03 at the Kazan State Technical University of Education at the address: 420015, Kazan, st. Karl Marx, d. 68 (conference room of the Academic Council). The dissertation can be found in the scientific library of the Kazan State Technological University. Abstract sent "___" April 2011 Scientific secretary of the dissertation council Tretyakova A.Ya. Copyright OJSC "Central Design Bureau "BIBCOM" & LLC "Agency Book-Service" 3 GENERAL CHARACTERISTICS OF THE WORK Topicality of the topic. The study of the regularities of the formation of heteroligand complexes in equilibrium systems is one of the main problems of coordination chemistry, which is inextricably linked with the implementation of innovative chemical technologies. The study of the complex formation of cobalt(II) and nickel(II) with complexones and dicarboxylic acids in aqueous solutions is very useful for substantiating and modeling chemical processes in polycomponent systems. Synthetic availability and wide possibilities of modification of these ligands create a great potential for creating complex-forming compositions based on them with the required set of properties. Information available in the literature on the coordination compounds of cobalt(II) and nickel(II) with the studied ligands is poorly systematized and incomplete for a number of ligands. There is practically no information on heteroligand complexation. Considering that the complexes of Co(II) and Ni(II) with the reagents under consideration have not been sufficiently studied, and the results obtained are very contradictory, the study of ionic equilibria in these systems and under the same experimental conditions is very important. Only taking into account all types of interactions can give an adequate picture of the state of equilibrium in complex multicomponent systems. In the light of the above considerations, the relevance of targeted and systematic studies of the processes of complex formation of cobalt(II) and nickel(II) salts with complexones and dicarboxylic acids for coordination chemistry seems obvious and significant. Work goals. Identification of equilibria and identification of features of the formation of homo- and heteroligand complexes of cobalt(II) and nickel(II) with monoamine carboxymethyl complexones and saturated dicarboxylic acids in aqueous solutions. To achieve the intended goal, the following tasks were set:  experimentally study the acid-base properties of the studied ligands, as well as the conditions for the formation of homo- and heteroligand complexes of cobalt(II) and nickel(II) in a wide range of pH values ​​and concentrations of reagents;  determine the stoichiometry of complexes in binary and ternary systems;  to carry out mathematical modeling of complex formation processes taking into account the completeness of all equilibria realized in the studied systems; Copyright OJSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" 4  to establish the ranges of pH values ​​for the existence of complexes and the share of their accumulation;  calculate the stability constants of the found complexes;  determine the constants of co-proportionalization of reactions and draw a conclusion about the compatibility of ligands in the coordination sphere of metal cations. Scientific novelty. For the first time, a systematic study of homo- and heteroligand complexes of cobalt(II) and nickel(II) with monoamine carboxymethyl chelators: iminodiacetic (IDA, H2Ida), 2-hydroxyethyliminodiacetic (HEIDA, H2Heida), nitrilothiacetic (NTA, H3Nta), methylglycindioacetic (MGDA, H3Mgda) acids and dicarboxylic acids of the limiting series: oxalic (H2Ox), malonic (H2Mal) and succinic (H2Suc). The interaction in solutions is considered from the standpoint of the multicomponent nature of the systems under study, which determines the presence of diverse competing reactions in the solution. New are the results of a quantitative description of homogeneous equilibria in systems containing cobalt(II) and nickel(II) salts, as well as monoamine complexones and dicarboxylic acids. The stoichiometry of heteroligand complexes was identified for the first time, the equilibrium constants of reactions and the stability constants of Co(II) and Ni(II) complexes with the studied ligands were determined. practical value. A substantiated approach to the study of the complex formation of cobalt(II) and nickel(II) with monoamine carboxymethyl complexones and dicarboxylic acids of the limiting series using various physicochemical methods of investigation is proposed. stability constants of homo- and heteroligand complexes of these metals. A comprehensive analysis of the studied systems in terms of stoichiometry and thermodynamic stability of cobalt(II) and nickel(II) complexes made it possible to establish some regularities between the structure of chelates and their complexing properties. This information can be useful in the development of quantitative methods for the determination and masking of the studied cations using complexing compositions based on complexones and dicarboxylic acids. The information obtained can be used to create technological solutions with desired properties and good performance characteristics. Copyright JSC "Central Design Bureau "BIBCOM" & OOO "Agency Kniga-Service" 5 The found values ​​of the reaction equilibrium constants can be taken as reference. The data obtained in the work are useful for using them in the educational process. The main provisions submitted for defense:  the results of the study of acid-base properties, protolytic equilibria and forms of existence of the studied ligands;  patterns of formation of homo- and heteroligand complexes of cobalt(II) and nickel(II) with monoamine carboxymethyl complexones and dicarboxylic acids under conditions of a variety of competing interactions;  results of mathematical modeling of equilibria in complex polycomponent systems according to spectrophotometry and potentiometry data;  the influence of various factors on the processes of complex formation in the systems under study;  stoichiometry of complexes, equilibrium constants of reactions, co-proportionation constants and stability constants of formed complexes, pH ranges of their formation and existence, as well as the effect of ligand concentrations on the share of accumulation of complexes. Personal contribution of the author. The author analyzed the state of the problem at the beginning of the study, formulated the goal, carried out the experimental work, took part in the development of the theoretical foundations of the subject of research, discussed the results and submitted them for publication. The main conclusions on the work carried out are formulated by the dissertation candidate. Approbation of work. The main results of the dissertation work were reported at the XXIV International Chugaev Conference on Coordination Compounds (St. Petersburg, 2009), the All-Russian Conference "Chemical Analysis" (Moscow - Klyazma, 2008), the IX Russian University Academic Scientific and Practical Conference (Izhevsk, 2008) , as well as at the annual final conferences of the Udmurt State University. Publications. The materials of the dissertation work are presented in 14 publications, including 6 abstracts of reports at All-Russian and International scientific conferences and 8 articles, among which 5 are published in journals included in the List of leading peer-reviewed scientific journals and publications recommended by the Higher Attestation Commission of the Ministry of Education and Science of Russia. Copyright OAO Central Design Bureau "BIBKOM" & OOO "Agency Book-Service" 6 Structure and volume of the dissertation. The dissertation work consists of an introduction, a literature review, an experimental part, a discussion of the results, conclusions and a list of references. The material of the work is presented on 168 pages, including 47 figures and 13 tables. The list of cited literature contains 208 titles of works by domestic and foreign authors. MAIN CONTENT OF THE WORK The study of the processes of complex formation was carried out by spectrophotometric and potentiometric methods. The optical density of solutions was measured on SF-26 and SF-56 spectrophotometers using a specially made Teflon cell with quartz glasses and an absorbing layer 5 cm thick. Such a cell makes it possible to simultaneously measure the pH value and the optical density of a solution. All curves A = f(pH) were obtained by spectrophotometric titration. Mathematical processing of the results was carried out using the CPESSP program. The study of complexation in binary and ternary systems was based on the change in the shape of the absorption spectra and the optical density of Co(II) and Ni(II) perchlorate solutions in the presence of complexones and dicarboxylic acids. In addition, we have constructed theoretical models of complexation for ternary systems without taking into account heteroligand complexation. In the course of comparing the theoretical dependences A = f(pH) with the experimental ones, deviations associated with the processes of formation of heteroligand complexes were revealed. Wavelengths of 500 and 520 nm for Co(II) compounds and 400 and 590 nm for Ni(II) were chosen as working wavelengths, at which the intrinsic absorption of ligands at different pH values ​​is insignificant, and complex compounds show a significant hyperchromic effect. When identifying equilibria, three constants of monomeric hydrolysis were taken into account for each of the metals. The dissociation constants of complexones and dicarboxylic acids used in the work are presented in Table 1. Monoamine carboxymethyl complexones can be represented as derivatives of iminodiacetic acid with the general formula HR + N CH2COO–CH2COOH where R: –H (IDA), –CH2CH2OH (HEIDA), –CH2COOH –CH (СH3)COOH (MGDA). (NTA) and Copyright OJSC "Central Design Bureau" BIBCOM " & LLC "Agency Kniga-Service" 7 Dicarboxylic acids of the limiting series used in the work can be represented by the general formula Cn H2n(COOH)2 (H2Dik). The nature of the dependence A = f(pH) for the M(II)–H2Dik systems showed that, as a rule, three +, , 2– complexes are formed in each of these systems, except for the M(II)–H2Suc system, in which bisdicarboxylates are not formed . We failed to establish the nature of the equilibrium in the Co(II)–H2Ox system, because at all pH values ​​poorly soluble precipitates of cobalt(II) oxalates precipitate, which makes it impossible to photometer the solution. Table 1. Protonation and dissociation constants of complexones and dicarboxylic acids at I = 0.1 (NaClO4) and Т = 20 ± 2°С 9.34 1.60 2.20 8.73 1.25 1.95 3.05 10.2 1.10 1.89 2.49 9.73 1.54 4.10 2.73 5.34 4.00 5.24 An increase in the pH of solutions leads to deprotonation and the formation of medium metal dicarboxylates. The complex is formed in region 3.0< рН < 8.0 и уже при соотношении 1: 1 имеет долю накопления 73%. Содержание комплекса 2– равно 14, 88 и 100% для 1: 1, 1: 2 и 1: 5 соответственно в области 3.0 < рН < 10.1. Аналогичные процессы протекают в системах M(II)–H2Mal. Увеличение концентрации малоновой кислоты сказывается на доле накопления комплекса , так для соотношения 1: 1 α = 60 % (6.3 < рН < 8.5), а для 1: 10 α = 72 % (2.0 < рН < 4.4). Содержание в растворе комплекса 2– возрастает c 64% до 91% для соотношений 1: 10 и 1: 50 (6.0 < рН 9.5). Максимальные доли накопления комплекса и 2– при оптимальных значениях рН составляют 70 и 80% для соотношения концентраций 1: 10 и 54 и 96% для 1: 50. Увеличение концентрации янтарной кислоты в системах M(II)–H2Suc способствует возрастанию долей накопления комплексов [МSuc] и [МHSuc]+ и смещению области их формирования в более кислую среду. Например, доли накопления комплекса при соотношении концентраций 1: 1, 1: 10 и 1: 40 соответственно равны 16, 68 и 90 %. Содержание комплексов Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 8 + и при соотношении 1: 50 равно 54% (рНопт. = 3.9) и 97% (рНопт. = 7.7) соответственно. Константы устойчивости дикарбоксилатов Co(II) и Ni(II), рассчитанные методом последовательных итераций приведены в таблице 2. Полученные нами величины хорошо согласуются с рядом литературных источников. Математическая обработка кривых A = f(pH) и α = f(pH) проведенная путем последовательного рассмотрения моделей равновесий с участием Co(II) и Ni(II) и моноаминных комплексонов (HxComp) показала, что во всех исследованных двойных системах типа M(II)–HxComp образуется несколько комплексов. В качестве примера на рис. 1 представлены кривые A = f(pH) для систем Co(II)–H2Heida (а) и Ni(II)–H2Heida (б). А а А б 0.5 0.4 3 0.4 3 4 0.3 4 5 0.3 1 0.2 0.2 0.1 0 5 2 0.1 0 2 4 6 8 10 рН 0 2 4 6 8 10 рН Рис. 1. Зависимость оптической плотности растворов от рН для кобальта(II) (1) и никеля(II) (2) и их комплексов с H2 Heida при соотношении компонентов 1: 1 (3), 1: 2 (4), 1: 5 (5), ССо2+ = 6∙10–3, СNi2+ = 8∙10–3 моль/дм3, λ = 520 (а), 400 нм (б). Методами насыщения и изомолярных серий установлено мольное соотношение компонентов в комплексонатах в зависимости от кислотности среды равное 1: 1 и 1: 2. Мольный состав комплексов подтвержден также методом математического моделирования. При эквимолярном соотношении компонентов стопроцентная доля накопления наблюдается только для комплексов – и –, а для комплексов , , и значения αmax равны 82, 98, 85 и 99% соответственно. В слабокислой среде монокомплексонаты Co(II) и Ni(II) присоединяют второй анион комплексона, образуя средние бискомплексонаты 2(1–x). При двукратном избытке комплексона максимальные доли накопления комплексов 2–, 2– и Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 9 4– находятся в пределах 88 – 99% для области 8.6 < рН < 11.6. В данном интервале рН накапливаются и комплексы 4– и 4–, для которых αmax достигает 56 и 72% соответственно. Одновременно с бискомплексонатами металлов в двойных системах, за исключением систем M(II)–H2Ida в щелочной среде образуется также гидроксокомплексы 1–x. Константы устойчивости комплексонатов Co(II) и Ni(II) представлены в таблице 2. Таблица 2. Области значений рН существования и константы устойчивости дикарбоксилатов и комплексонатов кобальта(II) и никеля(II) при I = 0.1 и Т = 20 ± 2°С Комплекс Области рН существования lg  Комплекс Области рН существования lg  + 2– + 2– + 2– 2– – – 4– 2– – – – 0.4–5.5 >1.9 >3.2 2.0–7.0 >3.6 2.4–12.0 >4.6 1.4–12.0 >4.8 >8.8 >1.0 >5.1 >9.8 5.46* 4.75* 6.91* 5.18 ± 0.06 2.97 ± 0.08 4.51 ± 0.08 6.29 ± 0.09 1.18 ± 0.09 11.69 ± 0.16 8.16 ± 0.14 12.28 ± 0.66 11.88 ± 0.37 10.10 ± 0.76 13.50 ± 0.12 12.50 ± 0.09 + 2– + 2– + 2– 2– – – 4– 2– 0.0–3.2 >0.2 >1.2 0.3– > 3.3 1.9-7.1> 2.8 1.2-5.9> 2.1 1.0-12.0> 3.7> 10.0> 0.8> 4.3> 9.6 6.30 ± 0.08 5.35 ± 0.08 9.25 ± 0.10 ± 0.07 3.50 ± 0.09 5.30 ± 0.07 6.39 ± 0.10 1.95 ± 0.08 8.44 ± 0.05 14.80 ± 0.08 9.33 ± 0.05 14.20 ± 0.06 12.05 ± 0.11 ± 0.05 ± 0.76 16.34 ± 0.05 13.95 ± 0.09 - 4- 2-> 1.1> 7.2> 10.5> 1.0> 7.0> 9.3 12.95 ± 0.13 16.29 ± 0.24 15.85 ± 0.58 11.27 ± 0.13 – 14.03 ± 0.35 4– 13.08 ± 0.72 2– *Literature data The processes of complexation in ternary systems also depend on the concentration of reagents and the acidity of the medium. For the formation of heteroligand complexes, the concentration of each of the ligands must be no less than their concentration in binary systems with the maximum accumulation of the homoligand complex. Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" 10 It was found that in all ternary systems, heteroligand complexes are formed with a molar ratio of 1: 1: 1 and 1: 2: 1, with the exception of systems M(II)–H2Ida –H2Dik, in which only 1:1:1 complexes are formed. The proof of the existence of heteroligand complexes was the fact that the theoretical curves A = f(pH) calculated without taking into account heteroligand complex formation noticeably differ from the experimental curves (Fig. 2.) A 0.3 . Fig. 2. Dependence of the optical density of solutions on pH for nickel(II) (1) and its complexes with H2Ida (2), H2Ox (3), H2Ida + H2Ox (4, 6), curve calculated without taking into account heteroligand complexes (5), at the ratio of components 1: 5 (2), 1: 2 (3), 1: 2: 2 (4, 5), 1: 2: 5 (6); СNi2+ = 8∙10–3 mol/dm3. 2 0.2 4 6 5 0.1 3 1 0 0 2 4 6 8 10 pH In the M(II)–H2Ida–H2Dik systems, the formation of three types of complexes –, 2–, and 3– is possible. Moreover, if the system contains oxalic acid, then Co(II) and Ni(II) oxalates act as structural particles. In ternary systems containing H2Mal or H2Suc, the role of the primary ligand is played by the iminodiacetates of these metals. Protonated complexes are formed only in the М(II)–H2Ida–H2Ox systems. Complexes – and – are formed in a strongly acid medium and in the range of 2.5< рН < 3.0 их содержание достигает 21 и 51% соответственно (для соотношения 1: 2: 2). В слабокислой среде кислые комплексы депротонируются с образованием средних гетеролигандных комплексов состава 2– и 2–, максимальные доли накопления которых при рН = 6.5 – 6.6 соответствеено равны 96 и 85% (для 1: 2: 2). При рН > 10.0 complex 2– is hydrolyzed to form 3–. Similar processes occur in the M(II)–H2Ida–H2Mal systems. Complexes 2– and 2– have the maximum accumulation fractions of 80 and 64% (for 1:2:10 and pH = 6.4). In an alkaline medium, the medium complexes are converted into hydroxocomplexes of the 3– type. Copyright OJSC Central Design Bureau BIBCOM & LLC Agency Kniga-Service 11 The equilibria in the M(II)–H2Ida–H2Suc systems are strongly shifted towards Co(II) and Ni(II) iminodiacetates even at large excesses of H2Suc. Thus, at a ratio of 1 : 2 : 50 in these systems, only medium complexes of composition 2– and 2– are formed, the content of which in the solution is 60 and 53%, respectively (рН = 6.4). In the M(II)–H2Heida–H2Dik systems, the formation of four types of complexes is possible: –, 2–, 4–, and 3– . The protonated heteroligand complex was found for both studied metals and all ligands, except for the – complex. Medium complexes 2– and 4– are formed in weakly acidic and alkaline media with a maximum accumulation fraction of 72 and 68% at pH = 5.8 and 9.5, respectively (for 1:2:1). Nickel(II) oxalates in HEIDA solution form heteroligand complexes with the compositions –, 2–, and 4–; The completeness of the formation of heteroligand complexes in the M(II)–H2 Heida–H2Mal system strongly depends on the H2Mal concentration. For example, in the Ni(II)–H2Heida–H2Mal system at a concentration ratio of 1 : 2 : 10, the maximum accumulation fractions of –, 2–, and 4– complexes are 46, 65, and 11% for pH 4.0, 6.0, and 10.5, respectively. With an increase in the concentration of malonic acid by a factor of 50, the proportions of accumulation of these complexes at the same pH values ​​increase, respectively, to 76, 84, and 31%. In the Co(II)–H2 Heida–H2Mal system at a component ratio of 1:2:75, the following transformations take place: – αmax = 85%, pH = 3.4 – H+ 2– αmax = 96%, pH = 6.5 + Heida2– 4– αmax = 52%, pH = 9.8 Heteroligand complexes in the M(II)–H2 Heida–H2Suc systems are formed only at large excesses of succinic acid. Thus, for a ratio of 1: 2: 100, the maximum accumulation fractions of complexes –, 2–, and 4– are 67 (рН = 4.8), 78 (рН = 6.4), and 75% (рН = 9.0), and for complexes –, 2–, and 4– – 4 (рН = 4.6), 39 (рН = 6.0), and 6% (рН = 9.0–13.0), respectively. Similar processes occur in the M(II)–H3Nta–H2Dik systems. In the presence of oxalic acid in an acidic medium, Co(II) and Ni(II) oxalates dominate in solution with a low content of 2– complexes. Closer to the neutral medium, medium heteroligan complexes 3– and 3– are formed with a maximum accumulation fraction of 78 and 12 90% for pH = 6. 9 and 6.4 respectively. In an alkaline medium with an excess of NTA, the reaction proceeds in two directions with the formation of complexes 4– and 6–. The latter are accumulated in large amounts, for example, the share of accumulation of complex 6– reaches 82% at pH = 7.0. The fractional distribution of complexes in the Co(II)–H3Nta–H2Mal system is shown in Fig. . 3. α, % d c a 80 b d b 60 b c c a 40 b d a c d d c d b c 20 a b aa 0 + pH = 2.3 – pH = 3.2 2– pH = 3.8 2– pH = 6.8 4– pH = 10.5 6– pH = 10.5 Fig. 3. Proportions of accumulation of complexes at different pH values ​​and different ratios of components: 1:2:5 (a), 1:2:20 (b), 1:2:40 (c), 1:2:80 (d) c the Co(II)–H3Nta–H2Mal system. In the M(II)–H3Nta–H2Suc systems, the structural ligand is H3Nta, and succinic acid plays the role of an additional ligand. An increase in the concentration of H2Suc leads to an increase in the proportion of accumulation of heteroligand complexes. Thus, an increase in the content of succinic acid from 0.0 to 0.12 mol/dm3 leads to an increase in the α value of complex 3– from 47 to 76%, while the content of protonated complex 2– increases from 34 to 63% (at pH = 4.3). Approximately in the same ratio, the share ratio of complexes 3– and 2– changes. In an alkaline medium, complexes 3– are attached by another H3Nta molecule, and complexes of composition 6– are formed. The maximum accumulation of complex 6– is 43% at pH = 10.3 for a ratio of 1:2:40. For the corresponding nickel(II) complex, α = 44% at pH = 10.0, for a ratio of 1:2:50. heteroligand complexes are hydrolyzed with the formation of hydroxo complexes of composition 4–. Copyright JSC "Central Design Bureau "BIBCOM" & OOO "Agency Kniga-Service" 13 Homoligand complexes in the M(II)–H3Nta–H2Suc systems are present only – and 4–, succinate complexes are not detected. Table 3. Stability constants of heteroligand complexes of cobalt(II) and nickel(II) with complexones and dicarboxylic acids for I = 0.1 (NaClO4) and Т = 20±2°С Complex H2Ox H2Mal H2Suc – 2– 3– – 2– 3– – 2– 4– 3– – 2– 4– 3– 2– 3– 6– 4– 2– 3– 6– 4– 2– 3– 4– 2– 3– 6 - 4- 14.90 ± 0.19 11.27 ± 0.66 - 17.38 ± 0.11 13.09 ± 0.10 ± 0.15 ± 1.74 ± 0.61 ± 0.15 ± 0.28 ± 0.61 ± 0.12 ± 0.28 ± 0.18 16.50 ± 0.20 ± 0.39 ± 0.23 ± 0.20 ± 0.31 12.31 ± 0.22 - 14.95 ± 0.09 17.60 ± 0.56 14.75 ± 0.24 18.98 ± 0.05 17.70 ± 0.09 16.99 ± 0.26 13.36 ± 0.73 15.73 ± 0.14 ± 0.25 ± 0.28 ± 0.19 - - 9.20 ± 0.27 10.40 ± 0.17 - 10. 76 ± 0.38 - 15.58 ± 0.28 11.07 ± 0.43 14.07 ± 1.09 14.18 ± 0.52 16.15 ± 0.19 ± 1.30 12.17 ± 0.68 ± 1.30 12.17 ± 0.68 ± 0.17 ± 0.34 ± 0.04 14.95 ± 0.09 16.93 ± 0.46 ± 0.10 ± 0.45 17.50 ± 0.16 15.85 ± 0.09 16.93 ± 0.47 11.92 ± 0.71 15.28 ± 0.94 - 13.93 ± 0.76 17.26 ± 0.72 16.65 ± 0.35 - 7.82 ± 0.66 - 9.61 ± 0.67 - 14.73 ± 0.43 9.49 ± 1.65 ± 1.53 ± 1.55 ± 0.79 9.77 ± 0.26 13.44 ± 0.47 - 16.84 ± 0.34 11.65 ± 0.17 15.50 ± 0.10 15.05 ± 0.03 17.79 ± 0.34 12.85 ± 0.18 17.03 ± 0.06 16.50 ± 0.13 ± 0.31 ± 0.34 ± 0.13 ± 0.95 - 12.93 ± 0.42 - 16.84 ± 0.73 COPYRIGHT OJSC "TsKB" Bibcom "& OOO Agency Kniga-Service 14 In the M(II)–H3Mgda–H2Dik systems, the formation of four types of complexes is also possible: 2–, 3–, 6–, and 4–. However, not all of these complexes are formed in individual systems. Both metals form protonated complexes in oxalic acid solutions, and Co(II) also forms in malonic acid solutions. The share of accumulation of these complexes is not large and, as a rule, does not exceed 10%. Only for complex 2– αmax = 21% at pH = 4.0 and component ratio 1:2:50. The content of complex 3– increases significantly with increasing concentration of oxalic acid. With a twofold excess of H2Ox, the share of accumulation of this complex is 43% in the region of 6.0< рН < 9.0, а при десятикратном она увеличивается до 80%. При рН >10.0, even at a high concentration of oxalate ions, this complex is hydrolyzed to form 4–. Nickel(II) complex 3– is formed in the region 6.4< рН < 7.9 и для соотношения компонентов 1: 2: 10 доля его накопления составляет 96%. При рН >7.0, another medium heteroligand complex of composition 6– is formed in the solution (α = 67% at pH temp. = 11.3). A further increase in the concentration of H2Ox has practically no effect on the value of α for these complexes. At a concentration ratio of 1:2:25, the accumulation shares of complexes 3– and 6– are 97 and 68%, respectively. The structural particle in the M(II)–H3Mgda–H2Ox systems is oxalic acid. On fig. Figure 4 shows the curves α = f(pH) and А = f(pH), which characterize the state of equilibrium in the M(II)–H3Mgda–H2Mal systems. The heteroligand complex formation in the M(II)–H3Mgda–H2Suc systems also strongly depends on the concentration of succinic acid. At a tenfold excess of H2Suc, heteroligand complexes are not formed in these systems. With a concentration ratio of 1: 2: 25 in the range of 6.5< рН < 9.0 образуются комплексы 3– (αmax = 10%) и 3– (αmax = 8%)/ Пятидесятикратный избыток янтарной кислоты увеличивает содержание этих комплексов до 15 – 16%. При стократном избытке H2Suc области значений рН существования комплексов 3– значительно расширяются, а максимальная доля накопления их возрастает приблизительно до 28 – 30%. Следует отметить, что для образования гетеролигандного комплекса в растворе необходимо определенное геометрическое подобие структур реагирующих гомолигандных комплексов, причем структура свойственная гомолигандному комплексу стабилизируется в гетеролигандном. Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 15 α 1.0 а А 2 4 1 6 3 0 2 7 6 8 б 2 10 A 4 1 0.3 0.2 5 4 1.0 0.4 9 0.5 α 0.2 6 0.5 8 7 0.1 рН 0.1 3 0 2 4 6 8 10 рН Рис. 4. Зависимость долей накопления комплексов (α) и оптической плотности растворов (A) от рН в системах Co(II)–H3Mgda–H2Mal (а) и Ni(II)–H3Mgda–H2Mal (б) для соотношения 1: 2: 50: экспериментальная кривая A = f(pH) (1), М2+ (2), [МHMal]+ (3), – (4), 2– (5), 3– (6), 4– (7), 6– (8), 4– (9); СCo2+ = 3∙10–3, СNi2+ = 4∙10–3 моль/дм3. Одним из факторов, определяющих стехиометрию и устойчивость гетеролигандных комплексов является совместимость лиганда в координационной сфере катиона металла. Мерой совместимости служит константа сопропорционирования Kd, характеризующая равновесия вида: 2(1–x) + 4– 2 x– В случае Kd > 1 (or lgKd > 0) ligands in the coordination sphere are compatible. For our set of heteroligand complexes, the Kd value (Kd = β2111/βMComp2βMDik2) is always greater than unity, which indicates the compatibility of the ligands in the Co(II) and Ni(II) coordination sphere. In addition, in all cases, the lgβ111 value of the heteroligand complex exceeds the geometric mean of the lgβ values ​​of the corresponding biscomplexes, which also indicates the compatibility of the ligands. CONCLUSIONS 1. A systematic study of homo- and heteroligand complexes of cobalt(II) and nickel(II) with monoamine carboxymethyl complexones (IDA, HEIDA, NTA, MGDA) and saturated dicarboxylic acids (oxalic, malonic, succinic) in aqueous solutions was carried out for the first time. 34 homoligand complexes were identified in 14 binary and 65 heteroligand complexes in 24 ternary systems. Copyright JSC "Central Design Bureau "BIBCOM" & LLC "Agency Kniga-Service" 16 2. The influence of various factors on the nature of protolytic equilibria and the completeness of the formation of complexes has been established. The accumulation fractions for all homo- and heteroligand complexes were calculated depending on the acidity of the medium and the concentration of the reacting components. The stoichiometry of the complexes was determined at different pH values, as well as the regions of their existence at different concentrations of ligands. 3. It has been established that in solutions of Co(II) and Ni(II) oxalates and malonates, there are three types of complexes + and 2–, while in solutions of succinates only two monocomplexes of + and composition are found. To increase the share of accumulation of dicarboxylates, a multiple increase in the content of dicarboxylic acids is required. In this case, not only the stoichiometry, but also the pH ranges of the existence of these complexes can change. 4. It has been shown that the stoichiometry of the complexes in the M(II) – HxComp systems depends on the acidity of the medium and the concentration of ligands. In acidic media, in all systems, complexes 2–x are first formed, which, in slightly acidic solutions, turn into biscomplexonates 2(1–x) with an increase in pH. A 100% accumulation of complexes requires a two to threefold excess of the ligand, while the formation of complexes shifts to a more acidic region. For the completeness of the formation of complexes - and - an excess of the complexone is not required. In an alkaline environment, complexonates are hydrolyzed with the formation of 1–x. 5. The equilibria of complex formation in the M(II)–HxComp–H2Dik ternary systems were studied for the first time and heteroligand complexes of composition 1–x, x–, 2x– and (1+x)– were found. It has been established that the fractions of accumulation of these complexes and the sequence of their transformation depend on the acidity of the medium and the concentration of the dicarboxylic acid. The compatibility of ligands in the coordination sphere of metal cations was established from the values ​​of coproportionation constants. 6. Two mechanisms of heteroligand complexation have been identified. The first of them is dicarboxylate-complexonate, in which the dicarboxylic acid anion plays the role of the primary structure-defining ligand. This mechanism is implemented in all systems of the M(II)–HxComp–H2Ox type, as well as in some M(II)–HxComp–H2Dik systems, where HxComp is H2Ida and H2 Heida, and H2Dik is H2Mal and H2Suc. The second mechanism is complexonatodicarboxylate, where the structure-setting ligand is a metal complexone or complexonate. This mechanism manifests itself in all systems M(II)–H3Comp–H2Dik, where H3Comp is H3Nta and H3Mgda, and H2Dik is H2Mal and Both mechanisms indicate the sequence of binding of the studied ligands into a heteroligand complex with an increase in pH. 7. The stability constants of homo- and heteroligand complexes have been calculated, the optimal ratios M(II) : H3Comp : H2Dik and the pH values ​​at which the concentrations of complex particles reach the maximum value have been determined. It was found that the logβ values ​​of homo- and heteroligand complexes increase in the series:< < , < < – < –, 2– ≈ 2– < 4– ≈ 4–, 2– < 2– < 3– < 3–, которые обусловлены строением, основностью и дентатностью хелатов, размерами хелатных циклов, а также величиной координационного числа металла и стерическими эффектами. Основные результаты диссертации опубликованы в ведущих журналах, рекомендованных ВАК: 1. 2. 3. 4. 5. Корнев В.И., Семенова М.Г., Меркулов Д.А. Однороднолигандные и смешанолигандные комплексы кобальта(II) и никеля(II) с нитрилотриуксусной кислотой и дикарбоновыми кислотами // Коорд. химия. – 2009. – Т. 35, № 7. – С. 527-534. Корнев В.И., Семенова М.Г. Физико-химические исследования равновесий в системах ион металла – органический лиганд. Часть 1. Взаимодействие кобальта(II) с 2-гидроксиэтилиминодиацетатом в водных растворах дикарбоновых кислот // Бутлеровские сообщения. – 2009. – Т.17, №5. – С.54-60. Семенова М.Г., Корнев В.И. Комплексонаты кобальта(II) и никеля(II) в водных растворах щавелевой кислоты // Химическая физика и мезоскопия. – 2010. – Т. 12, № 1. – С. 131-138. Корнев В.И., Семенова М.Г., Меркулов Д.А. Гетеролигандные комплексы кобальта(II) и никеля(II) с иминодиуксусной и дикарбоновыми кислотами в водном растворе // Коорд. химия. – 2010. – Т. 36, № 8. – С. 595-600. Семенова М.Г., Корнев В.И., Меркулов Д.А. Метилглициндиацетаты некоторых переходных металлов в водном растворе // Химическая физика и мезоскопия – 2010. – Т.12, № 3. – С.390-394. Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис» 18 в других изданиях: 6. 7. 8. 9. 10. 11. 12. 13. 14. Корнев В.И., Семенова М.Г. Гетеролигандные комплексы кобальта(II) с нитрилотриуксусной кислотой и дикарбоновыми кислотами // Вестник Удм. Университета. Физика. Химия – 2008. – № 2. – С. 65-72. Семенова М.Г., Корнев В.И, Меркулов Д.А. Исследование равновесий в водных растворах дикарбоксилатов кобальта(II) и никеля(II) // Всероссийская конференция «Химический анализ» – Тез. докл. – Москва-Клязьма, 2008 – С. 93-94. Корнев В.И., Семенова М.Г., Меркулов Д.А. Взаимодействие никеля(II) с нитрилотриуксусной кислотой в присутствии дикарбоновых кислот // Девятая Российская университетско-академическая научно-практическая конференция: Материалы конференции – Ижевск, 2008 – С. 103-105. Семенова М.Г., Корнев В.И. Смешанолигандное комплексообразование кобальта(II) с нитрилотриуксусной кислотой и дикарбоксилатами // Девятая Российская университетско-академическая научно-практическая конференция: Материалы конференции – Ижевск, 2008 – С. 107-109. Семенова М.Г., Корнев В.И. Гетеролигандные комплексы 2гидроксиэтилиминодиацетата кобальта(II) и дикарбоновых кислот // XXIV Международная Чугаевская конференция по координационной химии и Молодежная конференция-школа «Физико-химические методы в химии координационных соединений» – Санкт-Петербург, 2009. – С. 434-435. Корнев В.И., Семенова М.Г., Меркулов Д.А. Метилглициндиацетатные комплексы некоторых переходных металлов в водно-дикарбоксилатных растворах // Десятая Российская университетско-академическая научнопрактическая конференция: Материалы конференции – Ижевск, 2010 – С. 101-102. Корнев В.И., Семенова М.Г. Взаимодействие кобальта(II) и никеля(II) c комплексонами ряда карбоксиметиленаминов и малоновой кислотой в водном растворе // Вестник Удм. Университета. Физика. Химия. – 2010. – № 1. – С. 34-41. Корнев В.И., Семенова М.Г. Кислотно-основные и комплексообразующие свойства метилглициндиуксусной кислоты // Десятая Российская университетско-академическая научно-практическая конференция: Материалы конференции – Ижевск, 2010 – С. 104-105. Семенова М.Г., Корнев В.И. Метилглицинатные комплексы кобальта (II) и никеля(II) в водно-дикарбоксилатных растворах // Вестник Удм. Университета. Физика. Химия – 2010 – № 2. – С. 66-71.

Dicarboxylic acids form two series of functional derivatives - one and two carboxyl groups.

acid properties. With the accumulation of acid groups, the acid properties of the compounds increase. The acidity of dicarboxylic acids is greater than that of monocarboxylic acids. Thus, oxalic acid (pK a 1.23) is much stronger than acetic acid (pK a 4.76), which is associated with the -/- effect of the COOH group, and due to this, a more complete delocalization of the negative charge in the conjugate base.

The influence of the substituent is most clearly manifested when it is located close to the acid center.

Decarboxylation. When heated with sulfuric acid, oxalic acid decarboxylates, and the resulting formic acid decomposes further.

Malonic acid is easily decarboxylated when heated above 100°C.

Formation of cyclic anhydrides. In dicarboxylic acids containing four or five carbon atoms in the chain and therefore capable of being in a pincer conformation, functional groups converge in space. As a result of intramolecular attack by one carboxyl group (nucleophile) of the electrophilic center of another carboxyl group, a stable five or six-membered cyclic anhydride is formed (when heated), as shown in the examples of succinic and glutaric acids. In other words, dicarboxylic acid anhydrides are products intramolecular cyclization.

Maleic and fumaric acids exhibit similar chemical properties: they enter into reactions characteristic of compounds with a double bond (discoloration of bromine water, an aqueous solution of potassium permanganate) and compounds with carboxyl groups (they form two series of derivatives - acidic and medium salts, esters, etc. ). However, only one of the acids, namely maleic acid, under relatively mild conditions undergoes intramolecular cyclization with the formation of cyclic anhydride. In fumaric acid, due to the remoteness of carboxyl groups from each other in space, the formation of cyclic anhydride is impossible.

Succinic acid oxidation in vivo. Dehydrogenation (oxidation) of succinic acid to fumaric acid, catalyzed in the body by an enzyme, is carried out with the participation of the coenzyme FAD. The reaction proceeds stereospecifically with the formation of fumaric acid (in ionic form - fumarate).

3.1.4. Tautomerismβ -dicarbonyl compounds

A certain proton mobility of the hydrogen atom at the α-carbon atom in carbonyl compounds (weak CH-acid center) is manifested in their ability to undergo condensation reactions. If the mobility of such a hydrogen atom increases so much that it can split off in the form of a proton, then this will lead to the formation of a mesomeric ion (I), the negative charge of which is dispersed between carbon and oxygen atoms. The reverse addition of a proton to this ion, in accordance with its boundary structures, can lead either to the original carbonyl compound or to the enol.

In accordance with this, a carbonyl compound can exist in equilibrium with the isomer - enol form. This type of isomerism is called tautomerism and isomers in a state of mobile
balance, - tautomers.

Tautomerism is an equilibrium dynamic isomerism. Its essence lies in the mutual transformation of isomers with the transfer of any mobile group and the corresponding redistribution of electron density.

In the case under consideration, a proton transfer occurs between the ketone and enol forms, so this equilibrium is called prototropic tautomerism, in particular, keto-enol tautomerism.

In monocarbonyl compounds (aldehydes, ketones, esters), the equilibrium is almost completely shifted towards the ketone form. For example, the content of the enol form in acetone is only 0.0002%. In the presence of a second electron-withdrawing group at the α-carbon atom (for example, the second carbonyl group), the content of the enol form increases. Thus, in the 1,3-dicarbonyl compound acetylacetone (pentanedione-2,4), the enol form predominates.

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Smirnova Tatyana Ivanovna Study of the complexation of rare earth and other elements with some complexones, derivatives of isomers of diaminocyclohexane and dicarboxylic acids: il RGB OD 61:85-2 / 487

Introduction

1. About the complex, derivatives of diamino-cyclohexane and comixones, derivatives of djarboxonic acids 13

1.1. Synthesis of complexones 13

1.2. Acid dissociation constants 14

1.3. Complexes of alkaline earth metals and magnesium 16

1.4. Complexes of d - transitional and some other elements 19

1.5. REE complexes 23

2. Research methods 32

2.1. pH metric titration method 32

2.1.1. Determination of acid dissociation constants of tetrabasic acids 32

2.1.2. Potentiometric method for determining the stability constants of complexes 33

2.2. Indirect potentiometric method using a stationary mercury electrode 34

2.3. Indirect potentiometric method using a dripping copper amalgam electrode 36

2.4. Spectrographic method 38

3. Technique and methodology of the experiment 40

3.1. Synthesis of KPDK-DCG 40

3.1.1. Synthesis of trans-1,2-daaminocyclohexane-U»N-dimalonic acid 41

3.1.2. Synthesis of ods-1,3-diaminopyclohexane - N , N "- dimalonic acid 42

3.1.3. Synthesis of trans-1,4-diaminocyclohexane-N, N-dimalonic acid 43

3.1.4. Synthesis of cis-1,4-diaminocyclohexane-N, N-dimalonic acid 43

3.1.5. Synthesis of trans-1,2-diaminopyclohexane-N "N" - disuccinic acid 44

3.1.6. Physical properties of KPDK-DCG 45

3.2. Starting materials and devices used. 46

3.3. Mathematical processing of experimental results 47

4. Results of the study and their discussion 49

4.1. Determination of acid dissociation constants KPDK-DCH 49

4.2. Complexes of alkaline earth metals and magnesium with KPDK-DCH 53

4.3. Investigation of the complex formation of doubly charged ions of some metals with KPDK-DCH 55

4.3.1. Study of the complex formation of copper (P) with trans-1,2-DCGDMA by the lotenpyometric method 56

4.3.2, Study of the complex formation of TP* of mercury (P) with KPDK-DCH by the potentiometric method using a stationary mercury electrode 60

4.3.3. Complexation of zinc (її), cadmium (P), and lead (P) with trans-1,2-JJJ and trans-1,2-DdTDNA 64

4.4. Investigation of the complex formation of rare-earth elements with CFDC-LCT by the Bjerrum method 66

4.5. Investigation of the complex formation of rare-earth elements with trans-1,2-DCTdac and trans-1,2-dZhIDA by an indirect potentiometric method using a stationary mercury electrode 72

4.6. Investigation of the complex formation of neodymium (III) with trans-1,2-DCTdaC by the spectrographic method 77

4.7. Investigation of the complex formation of neodymium (III) with trans-1,2-DCGDNA by the spectrographic method

4.8. Some possibilities of practical application of KVDK-DCT.

Introduction to work

One of the most important tasks of chemical science is the search for new compounds that have a set of predetermined properties and are suitable for practical use in various areas of the national economy. In this regard, the synthesis and study of new complexones is of great interest.

The term "complexons" was proposed by G. Schwarzenbach in relation to polyaminopolyacetic acids containing iminodiacetate groups associated with various aliphatic and aromatic radicals C I] „ Subsequently, the name "complexons" was extended to compounds containing other acid groups instead of acetate: carboxyalkyl, alkylphosphonic, alkylaroon, alkylsulfonic.

At present, complexones are organic chelate-forming compounds that combine basic and acidic centers in the molecule and form strong complexes with cations, as a rule, soluble in water C 2 ] . Compounds of this class have already found wide application in analytical chemistry, biology, copper-one, various industries and agriculture. The most common complexones include imino-diacetic acid (VDA, complexone I) and its structural analogs: nitrilotriacetic acid (NTC, complexone її), ethylenediaminetetraacetic acid (EDTA, complexone III) and trans-1,2-diaminocyclohexanetetra-acetic acid (DCTTA , complexon IV) acids,

DCTTK stands out among the complexones with six donor atoms as the most effective chelating agent. The stability constants of its complexes with various metal ions are one to three orders of magnitude higher than those of EDTA. But a number of disadvantages (insignificant solubility in water, low selectivity, etc.) limit the practical use of complexons containing acetic acid residues as acid substituents.

At the same time, the information available in the literature about complexones of a new class - derivatives of dicarboxylic acids (DIC) C 4 - 6] indicates the presence of a number of valuable qualities in such compounds that distinguish them favorably from many well-known complexones. Of particular interest are CCCCs from an ecological point of view, as they undergo structural restructuring under relatively mild conditions, which dramatically reduces the risk of environmental shifts during their practical use.

Since complexones derived from isomers of diaminocyclohexane and dicarboxylic acids should be expected to combine high complexing ability with environmental safety, better solubility and other valuable properties inherent in PDCA, we undertook the present study, the objectives of which were: a) the synthesis of new complexones, derivatives isomers of DCT and dicarboxylic acids; b) study of the processes of complex formation of ions of certain metals with synthesized complexones.

It seemed interesting to follow, using the example of complexes with the participation of CCCC - DCH, how the isomerism of ligands affects the stability of complexes formed by ions of various metals (primarily rare-earth elements). Attention to rare earth elements is explained by the fact that compounds of these elements are being used more and more every year in science, technology and the national economy. In addition, it is known that one of the first areas of practical application of complexones was the separation of REE, and the search for more and more perfect reagents for this purpose has not lost its relevance.

The choice of initial products for the synthesis of new complexones (trans - 1,2 - , cis - 1,3 - trans - 1,4 - and cis - 1,4 - isomers of diaminocyclohexane) is explained by the fact that for 1,2 - and 1,4 -diaminocyclohexane trans-isomer is more stable than the cis-isomer, and for 1,3-diaminocyclohexane, the cis-form is more stable. In the molecules of these isomers, both amino groups occupy the equatorial position (e, e - form): trans-I,2-DCH cis-1,3-EDG trans-1,4-,1SH , and in cis-1,2-, trane-1,3 - and pis-1,4 - isomers of diaminocyclohexane, one of the amino groups occupies the axial position (e,a-form):

cis-1,2-DPG trans-1,3-LDH cis-1,4-DCH A complexon based on cis-1,4-DCH was synthesized in order to compare its properties with those of the trans~isomer.

The results of the study are presented in four chapters. The first two chapters (literature review) are devoted to analog complexones and research methods used in the work. The two chapters of the experimental part contain data on the synthesis and study of the complexing ability of new complexones. - ІЗ -

LITERATURE REVIEW

CHAPTER I

ON COMPLEXONS, DERIVATIVES OF DSHMINOCYCLO-HEXANE ISOMERS AND COMPLEXONS, DERIVATIVES OF DICARBOXIC ACIDS

Literature sources do not contain data on the preparation and properties of any complexones, derivatives of cyclic diamines and dicarboxylic acids, therefore, in the review of the literature, information on the closest analogues of the PDCA synthesized by us - DCG: trans-1,2-DCTC, 1,3- and 1 ,4 - DNTTK, as well as two representatives of the KPDK - EDDYAK and EDPShch.

1.1. Synthesis of complexones

Carboxylalkylation of amines is one of the most common methods for the synthesis of complexones [2] . Condensation of the corresponding diamines with monochloroacetic acid resulted in trans-1,2-DCHTC, 1,3-DCHTC ^CH 2 -C00Na / Shr Akl NaOH U MH 2 -C00Na (I.I) R + 4CI.-C00M. R «XNH^Ct

Whether the last two complexones are cis- or trans-isomers is unknown from the literature data. Obtaining trans-1, 2 - DCTTK is also possible by condensation of diamine with formaldehyde and sodium cyanide.

The first complexone of the KPDK class was EDDAK, obtained by Mayer by the interaction of 1,2-dibromoethane with aspartic acid in an alkaline medium. Later, other methods for the synthesis of this complexone were proposed: by the interaction of ethylenediamine with maleic acid C 5] or its esters [ib].

EDDOC C17-201 was obtained by condensation of ethylenediamine and monobromomalonic acid, as well as by the interaction of 1,2-dibromoethane with aminomalonic acid in an alkaline medium.

1.2. Acid dissociation constants

All complexones under consideration are tetrabasic acids; therefore, the general symbol H^L is adopted for them. Based on the works [2,6,11,20], we can talk about the betaine structure in aqueous solutions of derivatives of DCH and acetic acid isomers: ch z -coo- ns-sn

H^C-CH 2 trans-1,2-DCTG

H00C-CHn^ +

00C-CH 2 -^, Nn v n, s-sn "l n 2 s s-nh

H 2 C-CH 2 g 1,3-DCGZh

H00S-CH 2 \+ ooc-sn^^ ns-sno / \ z

NRS-SN TMNSG 2

CH 2 -C00 1,4-DTTSZH X ^ m ^ -sn, -coon and KCC - based on the works, they consider the existence of hydrogen bonds between protons and carboxyl groups of the malonate fragment: -n, which is confirmed by the insolubility of EDTG in acids.

I» 2. Complexes of alkaline earth metals and magnesium

The processes of complex formation of AEM and Mr ions with various ligands, including complexones, are of unflagging interest to researchers, since compounds of these elements play a significant role both in living and inanimate nature [24, 25] and, moreover, are widely used in chemical analysis [ 1,3 J .

The complexation of AEM and Mg ions with trans-1,2-DCTTA was studied by potentiometric and polarographic [27] methods. For 1,3- and 1,4-DCGTC, there are results of studying complexation only with Mo and Ca ions.

Table 1.2. The logarithms of the stability constants of the complexes of AEM and with trans-1,2-DCTTK, 1,3- and 1,4-DTTC Сії] t = 20С, ll = 0.1 (KN0 3 or KCL) t = 250

In the work [її] the same influence of the remoteness of iminodiacetate groups from each other is noted both in the series of alicyclic and in the series of aliphatic complexones. The stability constants of Ca and Mp complexes with 1,3- and 1,4-DCHTC are lower than the corresponding values ​​of tri- andes, which is apparently due to the rigid fixation of the iminodiacetic groups in the cyclohexane ring [2]. With an increase in the distance between the donor groups in the DCTTC isomers, the stability of the ML complexes decreases sharply and the tendency to form binuclear MgL complexes increases. The stability of the monoprotonated MHL complexes "" practically does not change. The authors of C2,3,II] explain these facts by a decrease in the denticity of complexoons in the series 1,2-DCTTC > 1,3-DCTC > 1,4-DCTC, as well as by the thermodynamic instability of chelate rings with more than six members.

The complex formation of ACH and Mg ions with EDTG and EDTG was studied by poten- tiometric and electrophoretic C 22 methods. Complexes of the composition MHL "» ML 2- and M^L were found in aqueous solutions. The stability constants of the complexes determined by different researchers are in satisfactory agreement. The logarithms of the stability constants of the detected complexes are given in Table 1.3.

The stability of AEM complexes with both CPDs decreases in the series Ca > Sr > Ba » This corresponds to an increase in the ionic radii of the metals and points to the predominantly ionic nature of the bonds in their complexes. Medium monocomplexes of SHM with EDTG are somewhat inferior in strength to the corresponding compounds with E.SHK. The reason for this phenomenon probably lies in the entropy effect, which is expressed in the fact that the probability of achieving an advantageous spatial configuration required for coordination with the metal ion is higher for the EDSLCA. In addition, the authors of [29] consider

Table 1.3. The logarithm of the stability constants of the complexes of ACHM and Mg 2+ with EDTG C5] and EDTG t = 25C, u = 0.1 (KN0 3) possible participation in coordination along with oC-carboxyl groups and &-carboxyl groups, which leads to the formation of six-membered chelate cycles that have less strength in AGM complexes than five-membered ones.

The Mg ion, in contrast to SHM, forms a stronger complex with EDTG than EDDH. The explanation for this fact is the more covalent nature of the bond in the magnesium complexes compared with the complexes formed by AGM, and the higher nitrogen basicity in EDCA than in EDTC.

Despite the fact that EDGI and EDTG are potentially hexadentate ligands, steric hindrances lead to the fact that only two carboxyl groups of each of the complexes are involved in coordination, while one carboxyl group of each aminomalonate (in EDPMK) or aminoacetate (in EDTG) ) of the fragment remains free C4,211, i.e. EDTC and

ED1AA act as tetradate ligands in AGM and magnesium complexes.

1.4. Complexes of 3d-transition and some other metals

The study of the complex formation of d - transition metals with various complexing agents is of great interest, because their complexes are widely used in the national economy, chemical analysis, electroplating and many other areas of practical activity.

Complex compounds of transition metals with trans-1,2-DCGTC were studied by potentiometric, polarographic. Data on the stability of the complexes are contained in Table 1.5.

As can be seen from Table. 1.4 and 1.5, the stability of complexes of 3x1-transition metals with trans-1,2-DCHTC, EDBA and EZDAK changes in the following order Mn 2+ Zn 2+ ,4TO is consistent with the Irvshgg-Williams-Yapimirsky series for complexes of 3d-transition metals with oxygen - and nitrogen-containing ligands and is explained, as is known, by the stabilization of complexes in the field of ligands in comparison with aquoions.

Based on an IR spectroscopic study of a complex

Table 1.5

Logarithms of the stability constants of complexes of some d-elements and lead (P) with EDSC (H 4 R) and EDSC (H 4 Z); t \u003d 25 C, | A \u003d 0.1 (KN0 3) cos Cu 2 and Ni 2+ with EDGE, schemes of the structure of the compound

Fig.1.1. Schematic representation of the structure of the complexes: a) H 2 CuL and b) ML 2 ", where H 4 L = EDBA and M 2+ = Ni 2+ or Cu 2 +

Greater stability of transition metal complexes with

ETC than with ETC, explained as increased dentin

EDTG , and the greater nitrogen basicity of this ligand . *

1.5. REE complexes

Lanthanum, lanthanides and yttrium, which are a special group of f-transition elements, are very similar in chemical properties and differ significantly from other f- and d-elements. The main differences between REEs are: a) charge conservation 3+ for all REEs; b) characteristic optical spectra, representing for lanthanides with unfilled f. - shells narrow bands, which are little affected by complexation; c) observance of special patterns (monotonicity or periodicity) in the change in properties with an increase in atomic number

A slight change in the ionic radii and some differences in properties due to the filling of the inner 4-shells with electrons in the REE series are more pronounced during complex formation in a change in the stability constants of the complexes. Therefore, the appearance of a large number of publications devoted to REE complexes and review papers systematizing information in this area is quite understandable.

The complexation of rare-earth elements with trans-1,2-DTTC was first studied by the indirect polarographic method. At 20°C and Na = 0.1, the stability constants of medium monocomplexes LnL" were determined for all rare-earth elements. By means of direct potentiometry, the dissociation constants of protonated LnHL complexes were determined.

According to the temperature dependence of the stability constants LnL ", the thermodynamic characteristics of the complexes were determined, the values ​​of which, along with the logarithms of the stability constants of the complexes LnL" and -negative logarithms of the acid dissociation constants, are given in Table 1.6.

The thermodynamic characteristics of trans-1,2-DCHTA complexes sharply differ from those of EDTA. If the complexation reaction in the case of EDTA is exothermic, then the complexation of most rare earth elements with trans-1,2-DCHTC proceeds with heat absorption, and only at the end of the series of rare earth elements the reaction becomes exothermic and occurs with a decrease in entropy (Тb-Lu). . h

The study of the PMR spectra of the La-5 "4" and Lu" 5 "1" complexes with trans-1,2-DCTTK revealed the presence of an unbound carboxyl group in the LaL" complex and the absence of one in the LuL" complex.

Spectrographic study of complex formation

Table 1.6. The logarithms of the stability constants, the negative logarithms of the acid dissociation constants, and the thermodynamic characteristics of the REE complexes with trans-1,2-DCTCA and, = 0.1 with trans-I,2-DCTCA made it possible to establish the existence of the EuL " complex in two forms with absorption bands 579, 7 nm and 580.1 nm In one case, the ligand exhibits a denticity of 5. The transition of the complex to another form is accompanied by the release of a water molecule from the inner sphere of the complex and an increase in the dentinity of the ligand to 6. In Eu-trans-1,2-DCGTC systems complexes of EuHL, EuHL 2 , EuL 2 , and Eu(0H)L~C50.53] were also found.

Thus, the change in the structure of complexes with trans-1,2-DTTC in the REE series was confirmed by the data of various studies* friend . This causes steric hindrances for the formation of four bonds with the oxygen atoms of the carboxyl groups. With a decrease in the radius for the last members of the REE series, it becomes possible for sweat Ln to enter between two nitrogen atoms and the closure of bonds with four carboxyl groups located on both sides of the plane ^ N - Ln - N About 1 Change in the values ​​of 1 g K j_ nl for REE complexes with trans-1,2-DCTC is shown in Fig. . 1.2. The reactions of formation and dissociation of Ln 3+ complexes with trans-1,2-DCHTC were studied, as well as the kinetics of the exchange reactions: LnL" + *Ln 3+ ^*LnL~ + Ln 3+ (1.4)

It has been established that the rate of the exchange reaction depends on the concentration of hydrogen ions and does not depend on the concentration of substituent metal ions, just as in the reaction, by polarographic, spectrographic methods, as well as by the proton resonance method. According to the results of the work, it is possible to form La 3+ _j Sd 5+ Dy 3+ Eu> T Tb

1.18 f-10 "1 Er 3 + yb 3 + (im") Ho 3+ bі 3+ Lu 3+

Rice. 1.2. The dependence of lgK LnL on the value of the REE ionic radius for the Ln 3+ complexes with trans-1,2-DCHF shows that the change in the stability of medium REE monocomplexes with EDBA and EDCA has the usual character: the general trend of increasing the stability of complexes from lanthanum to lutetium with a minimum attributable to for gadolinium (Fig. 1.3). Apparently, the structure of monoethylenediamine succinates, which is quite flexible and allows approaching the ligand in the La-Eu region, loses its flexibility in the Gd-Ho range, so the lg j^LnL values ​​(Table 1.7) do not increase in this region. llkia. -O mv Sd 3+ Dy 3+

1.02 3+ Sm "+ Eu 5" Tb Er 3+ Yb 3+ Tm 3+ Lu 3+ r " 10 -Chm* 1)

Fig, 1.3. Dependence of lg Kl u l on the value of the ionic radius with EDDNC (I) for complexes Ln and EHDDC (2)

The resumption of growth of the stability constants of heavy REE complexes (after Er) with EDCA is probably due to the appearance of a new flexible structure, which ensures the convergence of Ln 3+ and the ligand as the ionic radius decreases from Er 3+ and Lu 3+. Stability of the average yttrium monocomplex with EDPDC makes it possible to place it between similar compounds of terbium and dysprosium, which approximately corresponds to the radius of the Y 3+ C 64 3 ion.

Table 1.7, Logarithms of the stability constants of REE complexes with EDPS and EDVDC \K = 0.1 * t = 25C ​​* * t = 20C to lexam Ce and Pr 3+, but (iyu & w EDPS is 3 orders of magnitude lower than the corresponding value for EDPS (Table .1,7), As can be seen from the data in the table, the difference in the stability constants of the REE complexes with EDSCLC and EDSCZH is 2 at the beginning of the series, and - - 30 -

3 order. It was noted [59] that REE with EDSA form more stable, biligand complexes existing in a larger pH range than similar complexes with EDCA. The authors attribute this fact to the high coordination number of Lp 3+ ions and the reduced EDPS denticity, assuming it to be four.

Spectrographic study of the system Nd * - EDPS at a ratio of components 1:2 (C N(i 3+ =0.01 mol/l) in the pH range from 7 to 10.

Thus, the literature sources indicate that complexones, derivatives of ethylenediamine and dicarboxylic acids, are characterized by a significant complexing ability with respect to REE ions. REE: the largest and constant difference between the values ​​of the stability constants of the complexes of neighboring REE loft in cerium and ~ 0.1 units. lpft in the yttrium subgroups.

According to the authors, ligands of medium denticity, which form anions with a high charge, should be the most effective for separating REE mixtures. In order to obtain and study such ligands, the present work was carried out,

Acid dissociation constants

All complexones under consideration are tetrabasic acids, therefore, the general symbol H L is adopted for them. Based on the works [2,6,11,20], we can speak about the betaine structure in aqueous solutions of derivatives of DCH and acetic acid isomers: These elements play a significant role both in living and inanimate nature [24, 25] and, in addition, are widely used in chemical analysis [1,3 J . The complexation of AEM and Mg ions with trans-1,2-DCTTA was studied by potentiometric and polarographic [27] methods. For 1,3- and 1,4-DCGTC, there are results of studying complexation only with Mo and Ca ions. In the work [її] the same influence of the remoteness of iminodiacetate groups from each other is noted both in the series of alicyclic and in the series of aliphatic complexones. The stability constants of Ca and Mp complexes with 1,3- and 1,4-DCHTC are lower than the corresponding values ​​of tri- andes, which is apparently due to the rigid fixation of the iminodiacetic groups in the cyclohexane ring [2]. With an increase in the distance between the donor groups in the DCTTC isomers, the stability of the ML complexes decreases sharply and the tendency to form binuclear MgL complexes increases. The stability of the monoprotonated MHL complexes "" practically does not change. The authors of C2,3,II] explain these facts by a decrease in the denticity of complexoons in the series 1,2-DCTC 1,3-DCTC 1,4-DCTC, as well as by the thermodynamic instability of chelate rings with more than six members. The complex formation of ACH and Mg ions with EDTG and EDTG was studied by poten- tiometric and electrophoretic C 22 methods. Complexes of the composition MHL "" ML2- and ML were found in aqueous solutions. The stability constants of the complexes determined by different researchers are in satisfactory agreement. The logarithms of the stability constants of the detected complexes are given in Table 1.3. ionic radii of metals and indicates the predominantly ionic nature of the bonds in their complexes.

Medium monocomplexes of SHM with EDTG are somewhat inferior in strength to the corresponding compounds with E.SHK. The reason for this phenomenon probably lies in the entropy effect, which is expressed in the fact that the probability of achieving an advantageous spatial configuration required for coordination with the metal ion is higher for the EDSLCA. In addition, the authors of [29] consider it possible that, along with oC-carboxyl groups, α-carboxyl groups can participate in coordination, which leads to the formation of six-membered chelate cycles, which in AGM complexes have a lower strength than five-membered ones. The Mg ion, in contrast to SHM, forms a stronger complex with EDTG than EDDH. The explanation for this fact is the more covalent nature of the bond in the magnesium complexes compared with the complexes formed by AGM, and the higher nitrogen basicity in EDCA than in EDTC. Despite the fact that EDGI and EDTG are potentially hexadentate ligands, steric hindrances lead to the fact that only two carboxyl groups of each of the complexes are involved in coordination, while one carboxyl group of each aminomalonate (in EDPMK) or aminoacetate (in EDTG) ) of the fragment remains free C4,211, i.e. EDTG and ED1AJA act as tetradate ligands in AGM and magnesium complexes. 1.4. Complexes of 3d-transition and some other metals their complexes are widely used in the national economy, chemical analysis, electroplating and many other areas of practical activity. Complex compounds of transition metals with trans-1,2-DCGTC were studied by potentiometric, polarographic. For the complexes HMnL , HCoL" , HNLL , HCuL and HZnL, the anidolysis constants were calculated, respectively, equal to 2.8; 2; 2.2; 2 [271]. Complexes of the composition Cr H3L +, CrH2L, CrL and PbH2L were found in acidic solutions. Their stability constants were determined. The interaction was studied: "MHL" + M2+=!: M2L + H+, CI.2) where M2+ = Cuz+, Zn2+, Cd2+ It was found that asymmetric binuclear complexes are formed.The data on the stability of the complexes are given in Table 1.5.As can be seen from Tables 1.4 and 1.5, the stability of the complexes of 3x1-transition metals with trans-1,2-DCHTA, EDBA and EZDAK changes in the following order Mn2+ Fe2+ Co2+ Ni2+ Cu2+ Zn2+,4TO agrees with the Irvschg-Williams-Yapimirsky series for complexes of 3d-transition metals with oxygen- and nitrogen-containing ligands and is explained, as is known, by the stabilization of complexes in the field of ligands compared to aquoions. Based on an IR spectroscopic study, the complex lanthanum, lanthanides and yttrium, which are a special group of f-transition elements, are very similar in chemical properties and differ significantly from other f- and d-elements. The main differences between REEs are: a) charge conservation 3+ for all REEs; b) characteristic optical spectra, representing for lanthanides with unfilled f. - shells narrow bands, which are little affected by complexation; c) observance of special patterns (monotonicity or periodicity) in the change in properties with an increase in the atomic number C 6.48] .

Indirect potentiometric method using a stationary mercury electrode

The method is widely used to determine the stability constants of complexes of various metals with complexones due to the simplicity of the experiment and the simplicity of calculations. This method is based on the study of the equilibrium reaction: HgL + MZ+ =: ML2 "4 + Hg2+ . (2.14) The equilibrium state of this exchange reaction is fixed by a standard mercury electrode, which is reversible with respect to Hg 2+ ions. The Nernst equation describing the dependence of the mercury electrode potential on at 25°C it has the form: E = EQ + 0.02955 lg When studying complexation in solutions containing a large excess of the ligand with respect to Cu ions, the possibility of the formation of polynuclear complexes can be neglected.

Expression (2.27) is used to calculate the stability constant ft0 of the average monocomplex and the stability constants of the protonated CuHnLn "z complexes. of normal blackening, each absorption band of an aquoion or complex is characterized by the value V A, conventionally called the intensity of the band: A change in the pH of the solution and the concentration of the ligand causes a change in the concentration of the metal aquo ion and complexes and, consequently, the value of vA. As a result of determining v A at various pH values, one can get a data set y An = (1, where the first index denotes the number of the complex, and the second index denotes the number of the solution. By combining the Y An values ​​in pairs for different solutions, one can exclude the Z \ values ​​and express the concentration in each solution "When studying systems involving poly- dentate ligands neo it is necessary to know the number and form of the attached ligands, determined by the equations С 6 ] . that form of the ligand is included, the negative logarithm of the concentration r i _ c i i of which, depending on pH, changes symbately with 1o ----- [6] . Thus, the spectrographic method of investigation makes it possible, in the presence of several complexes in solution, to determine directly from experimental data the concentration, stability, and regions of existence of these complexes. All the complexones used in the work (KISCHK-DCG) were synthesized by us for the first time. The most difficult step in obtaining CDCC-ZHG, as in the case of already known complexones, is their isolation and purification. The difficulty of carrying out these operations is increased by the fact that KPDK is better than similar derivatives of acetic acid, soluble in water. In addition, in the synthesis and isolation of complexones derived from succinic acid, it should be taken into account that the presence of secondary nitrogen atoms in the complexone molecule in combination with ft-carboxyl groups favors the intramolecular cyclization of C18, 90] during heating, which proceeds for EDCA according to the scheme . Metals whose stability constants of complexes are known can be further used as auxiliary metals in studying the complexation of other elements using indirect methods based on competitive reactions. Especially often, copper (II) and mercury (Sch) are used as auxiliary metals, somewhat less often - lead (P), cadmium (P), zinc (P). 4.3.1. Investigation of the complexation of copper (P) with trans-1,2-DCTDZh (by the potency-pyometric method using CAE 2.3) makes it possible to determine directly from the experimental data both the concentration of the ligand in all its forms and the equilibrium concentration of metal ions, related to the SHV potential by the equation [H+] - 0 F0(CH+])- (50„ To find the stability constants of the remaining complexes formed in the system, expression 2.27 must be transformed: As in the case of F0(CH+1) , when [H+3 -O F tH ])-JL Thus, by calculating from the measurement results a series of Fi(tH+l) values ​​corresponding to different pH values, and then extrapolating them to CH+] = 0, one can find the value of ftt . Some results of the potentiometric study of complex formation in the Cu - trans-1,2-DZhDMA system at 2 pH 9 are given in Table 4.10. As can be seen from the data of Table 4.10, in the pH range of 4-7, the function F0 (tH + 3) does not depend on the pH of the solution. This indicates that in this region only the average CuLc complex is formed in the solution. As the pH value decreases, F0 () on the pH of the solution (Fig. 4.9) An increase in the values ​​of F0 (LH 1) is also noticeable at pH 7, which obviously indicates the participation of hydroxyl groups in the complex formation According to Table 4.10, the stability constants of the three detected complexes were calculated: "" and Cu(0H)L equal (in lpji units) to 11.57 ± 0.06, 18.90 ± 0.05 and 25.4 ± 0.1, respectively. with trans-1,2-DCGJ and EDBA (Table 1.5) indicates a greater strength of the trans-1,2-DCGJ complexes. -1,2-DCTTK (Table 1.4), Considering the increase in the basicity of nitrogen in the series of EDVDC trans-1,2-DTTC, Shch \ W trans-1,2-DTTC, we can assume that The difference in the stability of the CuL complex compared to EDCMA for trans-1,2-DCTDJ is achieved by increasing the basicity of nitrogen and the stabilizing effect of the cyclohexane ring.

Investigation of the complex formation of rare-earth elements with trans-1,2-DCTdac and trans-1,2-dZhIDZh by an indirect potentiometric method using a stationary mercury electrode

The results of the study outlined above (p. 4.4) showed that the method of direct pH - potentiometric titration, which gives reliable results only provided that complexes of low or medium stability are formed in the systems under study. Therefore, to determine the stability constants of the averages. REE monocomplexes with trans-ї,2-DCGDMA and trans-1,2-DCHDNAA, an indirect potentiometric method was applied using a stationary mercury electrode (paragraphs 2.2,4.2.3). Some of the curves obtained for the dependence of the potential of the mercury electrode E on the pH of solutions containing trans-1,2-DCGdaC and trans-1,2-DCGDAC as ligands are shown in Fig. 4.16 and 4.17, respectively. As can be seen from the figures, all the presented curves have isopotential segments, indicating the existence of only medium complexes of mercury (II) and REE in the corresponding pH range. Knowing the value of E corresponding to the isopotential region and the stability constant of the complex of HgL 2 with the complexones under study, we can calculate the stability constants JiLnL of the REE under study. The values ​​of the logarithms of stability constants for REE and yttrium complexes with trans-1,2-DCTDMA and trans-1,2-DCDNAA are given in Table 4.15. As can be seen from the data in Table 4.15,. the stability of REE complexes with both complexones increases quite sharply in the cerium subgroup, while in the yttrium subgroup it increases slightly. A possible explanation for this phenomenon can be the gradual approach of the ligand to the Ln ion as 1/r increases (r is the ionic radius) in the case of light REE from La to Sm, and the cessation of this approach, associated with the exhaustion of the "flexibility" of the ligand, while structure of complexes in the series REE - tnsh transition from Sm to Lu y, this phenomenon indicates an increased covalence of bonds: in REE complexes with these complexoons. Apparently, the increased covalence of bonds is a common property of metal complexes with all complexoons derived from malonic acid [4, 59].

In terms of stability, the Y3+ complex with trans-1,2-DCSHAA can be placed in front of the Th 3+ complex, therefore, C 49 I, the bonds in the REE-complexes with these ligands are characterized by a lower covalence than with trans-1,2-DCSCHALS. The REE complexes with trans-1,2-DTVDShK, despite the somewhat higher basicity of nitrogen in the molecules of this ligand, are inferior in stability to the corresponding trans-1,2-DCGJ complexes. If this phenomenon were caused only by the different sizes of the chelate rings in the trans-1,2-DCGJ and trans-1,2-DCTG complexes, then piclohexadiamide sucpinates would have to be more stable. REE, because [4,18,23,70] shows a higher strength of six-membered chelate rings compared to five-membered ones in REE complexes with complexoons derived from ethylenediamine and carboxylic acids. trans-1,2-DCVDC in complexes with REE. However, the data of the potentiometric study do not contain direct information about the denticity of the complexoons and, consequently, about the structure of the complexes. Based on the results obtained by the pH-potentiometric method (paragraphs 4.4 and 4.5), it was suggested that the denticity of trans-1,2-dsq DMA in complexes with metal ions is reduced. This section presents the results of a spectrographic study of neodymium with trans-1,2-DCGDMA, which makes it possible to determine the amount of complexes formed, their composition, structure, and denticity of the L 49 ligand]. The study of the complex formation of neodymium with α-trans-1,2-DCHDDOK was carried out at various ratios of metal and ligand. The absorption spectra of solutions with a ratio of Nd 5+ : trans-1,2-JJJ = 1:1 in the range of K pH 12 and with a ratio of 1:2 and 1:3- in the region of 3.5 pH 12 are shown in Fig.4.18. As can be seen from Fig. 4.19, four absorption bands are observed in the absorption spectra: 427.3, 428.8, 429.3 and 430.3 nm. The complexation of the ligand with the neodymium ion begins already from the strongly acidic region and the absorption band of the neodymium aquo ion (427.3 nm) disappears at pH 1.2 with the appearance of an absorption band of the complex of equimolar composition (428.8 nm).

Calculation of the stability constants of this average complex and, possibly, the protonated pH formed in this region. complexes were not carried out, - t.ts. the simultaneous existence of a neodymium aquo ion and the complex in solution is observed in a very narrow pH range. However, using the data of a pH-potentiometric study of REE complexes (pp. 4.4 and 4.5), we can assume that the absorption band at 428.8 nm, which dominates in a wide range of 2 pH 9, refers to the medium complex composition of NdL _. The band at 430.3 nm observed in this system apparently refers to a complex with an increased denticity of the ligand. At pH 9.0, a new absorption band (429.3 nm) appears in the absorption spectra of the Ncl: trans-1,2-DCGJ = 1:1 system, which becomes dominant at pH 10.0. It could be assumed that this band corresponds to the hydroxo complex, the concentration of which is higher in the alkaline pH region. However, the calculation of the stability constant of this complex under this assumption showed the presence of a systematic change in its value by a factor of 100, i.e., that this assumption is incorrect. Obviously, the observed absorption band refers to the complex of equimolar composition, since as the ligand concentration increases, its intensity does not increase. To determine the denticity of trans-I,2-D1TSUSH in a complex with neodymium (III) with a composition of 1:1, the shift of the corresponding band to the long wavelength region was determined compared to the neodymium aquo ion. The value of the long-wavelength shift in the absorption spectra during the formation of complexes depends on the number of donor groups attached by the metal ion, and is a constant value for one type of ligand. The displacement increment is 0.4 nm per donor group. In order to assign the absorption bands of the system under study, we compared the absorption spectra of the systems III:SCH, where Hb = EDCC, EJC 6.104], EDPSCH G23], EDDA, ​​or trans-1,2-DSLC C105] . Since the listed complexones have the same donor beads, it can be expected that with the same number of these groups in the inner sphere of the complexes, the position of the absorption bands in the spectra should coincide. The absorption band at 428.8 nm found in the spectra of the systems Kd3+: EDSA, Nd3+: EDSA, Nd3: EDCYAC 23.67-72] is assigned by the authors to a monocomplex, where the denticity of the ligand is equal to four. Based on this, it can be assumed that in the absorption spectra of the Nd:trans-1,2-DCTD1C systems, this band also corresponds to the NdL monocomplex with the ligand denticity equal to four. In the acid region (pH = 1.02), this band coincides with the absorption bands of protonated NdHnLn"1 complexes, where the ligand is also tetradentate.

Tolkacheva, Lyudmila Nikolaevna

General chemistry: textbook / A. V. Zholnin; ed. V. A. Popkova, A. V. Zholnina. - 2012. - 400 p.: ill.

Chapter 7. COMPLEX COMPOUNDS

Chapter 7. COMPLEX COMPOUNDS

The complexing elements are the organizers of life.

K. B. Yatsimirsky

Complex compounds are the most extensive and diverse class of compounds. Living organisms contain complex compounds of biogenic metals with proteins, amino acids, porphyrins, nucleic acids, carbohydrates, and macrocyclic compounds. The most important processes of vital activity proceed with the participation of complex compounds. Some of them (hemoglobin, chlorophyll, hemocyanin, vitamin B 12, etc.) play a significant role in biochemical processes. Many drugs contain metal complexes. For example, insulin (zinc complex), vitamin B 12 (cobalt complex), platinol (platinum complex), etc.

7.1. COORDINATION THEORY OF A. WERNER

The structure of complex compounds

During the interaction of particles, mutual coordination of particles is observed, which can be defined as the process of complex formation. For example, the process of hydration of ions ends with the formation of aqua complexes. Complex formation reactions are accompanied by the transfer of electron pairs and lead to the formation or destruction of higher-order compounds, the so-called complex (coordination) compounds. A feature of complex compounds is the presence in them of a coordination bond that arose according to the donor-acceptor mechanism:

Complex compounds are compounds that exist both in the crystalline state and in solution.

which is the presence of a central atom surrounded by ligands. Complex compounds can be considered as complex compounds of a higher order, consisting of simple molecules capable of independent existence in solution.

According to Werner's coordination theory, in a complex compound, internal and outer sphere. The central atom with its surrounding ligands form the inner sphere of the complex. It is usually enclosed in square brackets. Everything else in a complex compound is the outer sphere and is written in square brackets. A certain number of ligands is placed around the central atom, which is determined coordination number(kch). The number of coordinated ligands is most often 6 or 4. The ligand occupies a coordination site near the central atom. Coordination changes the properties of both the ligands and the central atom. Often, coordinated ligands cannot be detected using chemical reactions characteristic of them in the free state. More tightly bound particles of the inner sphere are called complex (complex ion). Attraction forces act between the central atom and ligands (a covalent bond is formed according to the exchange and (or) donor-acceptor mechanism), and repulsive forces act between ligands. If the charge of the inner sphere is 0, then there is no outer coordination sphere.

Central atom (complexing agent)- an atom or ion that occupies a central position in a complex compound. The role of a complexing agent is most often performed by particles that have free orbits and a sufficiently large positive nuclear charge, and therefore can be electron acceptors. These are cations of transition elements. The strongest complexing agents are elements of groups IB and VIIIB. Rarely as a complex

neutral atoms of d-elements and non-metal atoms in various degrees of oxidation - . The number of free atomic orbitals provided by the complexing agent determines its coordination number. The value of the coordination number depends on many factors, but usually it is equal to twice the charge of the complexing ion:

Ligands- ions or molecules that are directly associated with the complexing agent and are donors of electron pairs. These electron-rich systems, which have free and mobile electron pairs, can be electron donors, for example:

Compounds of p-elements exhibit complexing properties and act as ligands in a complex compound. Ligands can be atoms and molecules (protein, amino acids, nucleic acids, carbohydrates). According to the number of bonds formed by ligands with the complexing agent, ligands are divided into mono-, di-, and polydentate ligands. The above ligands (molecules and anions) are monodentate, since they are donors of one electron pair. Bidentate ligands include molecules or ions containing two functional groups capable of being a donor of two electron pairs:

Polydentate ligands include the 6-dentate ligand of ethylenediaminetetraacetic acid:

The number of places occupied by each ligand in the inner sphere of the complex compound is called coordination capacity (denticity) of the ligand. It is determined by the number of electron pairs of the ligand that participate in the formation of a coordination bond with the central atom.

In addition to complex compounds, coordination chemistry covers double salts, crystalline hydrates, which decompose in an aqueous solution into constituent parts, which in the solid state in many cases are constructed similarly to complex ones, but are unstable.

The most stable and diverse complexes in terms of composition and the functions they perform form d-elements. Of particular importance are complex compounds of transition elements: iron, manganese, titanium, cobalt, copper, zinc and molybdenum. Biogenic s-elements (Na, K, Mg, Ca) form complex compounds only with ligands of a certain cyclic structure, also acting as a complexing agent. Main part R-elements (N, P, S, O) is the active active part of complexing particles (ligands), including bioligands. This is their biological significance.

Therefore, the ability to complex formation is a common property of the chemical elements of the periodic system, this ability decreases in the following order: f> d> p> s.

7.2. DETERMINATION OF THE CHARGE OF MAIN PARTICLES OF A COMPLEX COMPOUND

The charge of the inner sphere of a complex compound is the algebraic sum of the charges of its constituent particles. For example, the magnitude and sign of the charge of a complex are determined as follows. The charge of the aluminum ion is +3, the total charge of the six hydroxide ions is -6. Therefore, the charge of the complex is (+3) + (-6) = -3 and the formula of the complex is 3- . The charge of the complex ion is numerically equal to the total charge of the outer sphere and is opposite in sign to it. For example, the charge of the outer sphere K 3 is +3. Therefore, the charge of the complex ion is -3. The charge of the complexing agent is equal in magnitude and opposite in sign to the algebraic sum of the charges of all other particles of the complex compound. Hence, in K 3 the charge of the iron ion is +3, since the total charge of all other particles of the complex compound is (+3) + (-6) = -3.

7.3. NOMENCLATURE OF COMPLEX COMPOUNDS

The basics of nomenclature are developed in the classic works of Werner. In accordance with them, in a complex compound, the cation is first called, and then the anion. If the compound is of a non-electrolyte type, then it is called in one word. The name of the complex ion is written in one word.

The neutral ligand is named the same as the molecule, and an "o" is added to the anion ligands. For a coordinated water molecule, the designation "aqua-" is used. To indicate the number of identical ligands in the inner sphere of the complex, the Greek numerals di-, tri-, tetra-, penta-, hexa-, etc. are used as a prefix before the name of the ligands. The prefix monone is used. The ligands are listed in alphabetical order. The name of the ligand is considered as a single entity. After the name of the ligand, the name of the central atom follows, indicating the degree of oxidation, which is indicated by Roman numerals in parentheses. The word ammine (with two "m") is written in relation to ammonia. For all other amines, only one "m" is used.

C1 3 - hexamminecobalt (III) chloride.

C1 3 - aquapentamminecobalt (III) chloride.

Cl 2 - pentamethylamminechlorocobalt (III) chloride.

Diamminedibromoplatinum (II).

If the complex ion is an anion, then its Latin name has the ending "am".

(NH 4) 2 - ammonium tetrachloropalladate (II).

K - potassium pentabromoammineplatinate (IV).

K 2 - potassium tetrarodanocobaltate (II).

The name of a complex ligand is usually enclosed in parentheses.

NO 3 - dichloro-di-(ethylenediamine) cobalt (III) nitrate.

Br - bromo-tris-(triphenylphosphine) platinum (II) bromide.

In cases where the ligand binds two central ions, the Greek letter is used before its nameμ.

Such ligands are called bridge and listed last.

7.4. CHEMICAL BOND AND STRUCTURE OF COMPLEX COMPOUNDS

The donor-acceptor interactions between the ligand and the central atom play an important role in the formation of complex compounds. The electron pair donor is usually a ligand. An acceptor is a central atom that has free orbitals. This bond is strong and does not break when the complex is dissolved (nonionogenic), and it is called coordination.

Along with o-bonds, π-bonds are formed by the donor-acceptor mechanism. In this case, the metal ion serves as a donor, donating its paired d-electrons to the ligand, which has energetically favorable vacant orbitals. Such relationships are called dative. They are formed:

a) due to the overlap of the vacant p-orbitals of the metal with the d-orbital of the metal, on which there are electrons that have not entered into a σ-bond;

b) when the vacant d-orbitals of the ligand overlap with the filled d-orbitals of the metal.

A measure of its strength is the degree of overlap between the orbitals of the ligand and the central atom. The orientation of the bonds of the central atom determines the geometry of the complex. To explain the direction of bonds, the concept of hybridization of atomic orbitals of the central atom is used. Hybrid orbitals of the central atom are the result of mixing unequal atomic orbitals, as a result, the shape and energy of the orbitals change mutually, and orbitals of a new identical shape and energy are formed. The number of hybrid orbitals is always equal to the number of original ones. Hybrid clouds are located in the atom at the maximum distance from each other (Table 7.1).

Table 7.1. Types of hybridization of atomic orbitals of a complexing agent and the geometry of some complex compounds

The spatial structure of the complex is determined by the type of hybridization of valence orbitals and the number of unshared electron pairs contained in its valence energy level.

The efficiency of the donor-acceptor interaction between the ligand and the complexing agent, and, consequently, the strength of the bond between them (stability of the complex) is determined by their polarizability, i.e. the ability to transform their electron shells under external influence. On this basis, the reagents are divided into "hard" or low polarizable, and "soft" - easily polarizable. The polarity of an atom, molecule or ion depends on their size and the number of electron layers. The smaller the radius and electrons of a particle, the less polarized it is. The smaller the radius and the fewer electrons a particle has, the worse it polarizes.

Hard acids form strong (hard) complexes with electronegative O, N, F atoms of ligands (hard bases), while soft acids form strong (soft) complexes with donor P, S, and I atoms of ligands having low electronegativity and high polarizability. Here we see manifestation general principle"like with like".

Due to their rigidity, sodium and potassium ions practically do not form stable complexes with biosubstrates and are found in physiological media in the form of aquacomplexes. Ions Ca 2 + and Mg 2 + form quite stable complexes with proteins and therefore in physiological media are in both ionic and bound states.

Ions of d-elements form strong complexes with biosubstrates (proteins). And soft acids Cd, Pb, Hg are highly toxic. They form strong complexes with proteins containing R-SH sulfhydryl groups:

The cyanide ion is toxic. The soft ligand actively interacts with d-metals in complexes with biosubstrates, activating the latter.

7.5. DISSOCIATION OF COMPLEX COMPOUNDS. STABILITY OF COMPLEXES. LABILE AND INERT COMPLEXES

When complex compounds are dissolved in water, they usually decompose into ions of the outer and inner spheres, like strong electrolytes, since these ions are bound ionogenically, mainly by electrostatic forces. This is estimated as the primary dissociation of complex compounds.

The secondary dissociation of a complex compound is the disintegration of the inner sphere into its constituent components. This process proceeds according to the type of weak electrolytes, since the particles of the inner sphere are connected nonionically (covalently). Dissociation has a stepwise character:

For a qualitative characteristic of the stability of the inner sphere of a complex compound, an equilibrium constant is used that describes its complete dissociation, called complex instability constant(Kn). For a complex anion, the expression for the instability constant has the form:

The smaller the value of Kn, the more stable is the inner sphere of the complex compound, i.e. the less it dissociates in aqueous solution. Recently, instead of Kn, the value of the stability constant (Ku) is used - the reciprocal of Kn. The larger the Ku value, the more stable the complex.

The stability constants make it possible to predict the direction of ligand exchange processes.

In an aqueous solution, the metal ion exists in the form of aqua complexes: 2+ - hexaaqua iron (II), 2 + - tetraaqua copper (II). When writing formulas for hydrated ions, the coordinated water molecules of the hydration shell are not indicated, but implied. The formation of a complex between a metal ion and some ligand is considered as a reaction of substitution of a water molecule in the inner coordination sphere by this ligand.

Ligand exchange reactions proceed according to the mechanism of S N -type reactions. For instance:

The values ​​of the stability constants given in Table 7.2 indicate that due to the process of complex formation, strong binding of ions in aqueous solutions occurs, which indicates the effectiveness of using this type of reaction for binding ions, especially with polydentate ligands.

Table 7.2. Stability of zirconium complexes

Unlike ion exchange reactions, the formation of complex compounds is often not a quasi-instantaneous process. For example, when iron (III) reacts with nitrile trimethylenephosphonic acid, the equilibrium is established after 4 days. For the kinetic characteristics of complexes, the concepts are used - labile(fast reacting) and inert(slowly reacting). According to G. Taube, labile complexes are considered to be those that completely exchange ligands for 1 min at room temperature and a solution concentration of 0.1 M. It is necessary to clearly distinguish between thermodynamic concepts [strong (stable) / fragile (unstable)] and kinetic [ inert and labile] complexes.

In labile complexes, ligand substitution occurs rapidly and equilibrium is quickly established. In inert complexes, ligand substitution proceeds slowly.

So, the inert complex 2 + in an acidic medium is thermodynamically unstable: the instability constant is 10 -6 , and the labile complex 2- is very stable: the stability constant is 10 -30 . Taube associates the lability of complexes with the electronic structure of the central atom. The inertness of complexes is characteristic mainly of ions with an incomplete d-shell. Inert complexes include Co, Cr. Cyanide complexes of many cations with an external level of s 2 p 6 are labile.

7.6. CHEMICAL PROPERTIES OF COMPLEXES

The processes of complex formation affect practically the properties of all particles forming the complex. The higher the strength of the bonds between the ligand and the complexing agent, the less the properties of the central atom and ligands manifest themselves in the solution, and the more pronounced the features of the complex.

Complex compounds exhibit chemical and biological activity as a result of the coordination unsaturation of the central atom (there are free orbitals) and the presence of free electron pairs of ligands. In this case, the complex has electrophilic and nucleophilic properties that differ from those of the central atom and ligands.

It is necessary to take into account the influence on the chemical and biological activity of the structure of the hydration shell of the complex. The process of education

The reduction of complexes affects the acid-base properties of the complex compound. The formation of complex acids is accompanied by an increase in the strength of the acid or base, respectively. So, when complex acids are formed from simple ones, the binding energy with H + ions decreases and the strength of the acid increases accordingly. If there is an OH - ion in the outer sphere, then the bond between the complex cation and the hydroxide ion of the outer sphere decreases, and the basic properties of the complex increase. For example, copper hydroxide Cu (OH) 2 is a weak, sparingly soluble base. Under the action of ammonia on it, copper ammonia (OH) 2 is formed. The charge density of 2 + decreases compared to Cu 2 +, the bond with OH - ions is weakened, and (OH) 2 behaves like a strong base. The acid-base properties of the ligands associated with the complexing agent are usually more pronounced than the acid-base properties of them in the free state. For example, hemoglobin (Hb) or oxyhemoglobin (HbO 2) exhibit acidic properties due to the free carboxyl groups of the globin protein, which is a ligand of HHb ↔ H + + Hb - . At the same time, the hemoglobin anion, due to the amino groups of the globin protein, exhibits basic properties and therefore binds the acidic CO 2 oxide to form the carbaminohemoglobin anion (HbCO 2 -): CO 2 + Hb - ↔ HbCO 2 - .

The complexes exhibit redox properties due to redox transformations of the complexing agent, which forms stable oxidation states. The process of complexation strongly affects the values ​​of the reduction potentials of d-elements. If the reduced form of the cations forms a more stable complex with the given ligand than its oxidized form, then the value of the potential increases. A decrease in the potential value occurs when the oxidized form forms a more stable complex. For example, under the action of oxidizing agents: nitrites, nitrates, NO 2 , H 2 O 2, hemoglobin is converted into methemoglobin as a result of oxidation of the central atom.

The sixth orbital is used in the formation of oxyhemoglobin. The same orbital is involved in the formation of a bond with carbon monoxide. As a result, a macrocyclic complex with iron is formed - carboxyhemoglobin. This complex is 200 times more stable than the iron-oxygen complex in heme.

Rice. 7.1. Chemical transformations of hemoglobin in the human body. Scheme from the book: Slesarev V.I. Fundamentals of Living Chemistry, 2000

The formation of complex ions affects the catalytic activity of complexing ions. In some cases, activity is increasing. This is due to the formation in solution of large structural systems that can participate in the creation of intermediate products and a decrease in the activation energy of the reaction. For example, if Cu 2+ or NH 3 is added to H 2 O 2, the decomposition process is not accelerated. In the presence of the 2+ complex, which is formed in an alkaline medium, the decomposition of hydrogen peroxide is accelerated by 40 million times.

So, on hemoglobin, one can consider the properties of complex compounds: acid-base, complex formation and redox.

7.7. CLASSIFICATION OF COMPLEX COMPOUNDS

There are several classification systems for complex compounds based on different principles.

1. According to the belonging of a complex compound to a certain class of compounds:

Complex acids H 2 ;

Complex bases OH;

Complex salts K 4 .

2. By the nature of the ligand: aqua complexes, ammoniates, acido complexes (anions of various acids, K 4, act as ligands; hydroxo complexes (hydroxyl groups, K 3, as ligands); complexes with macrocyclic ligands, inside which central atom.

3. By the sign of the charge of the complex: cationic - complex cation in the complex compound Cl 3; anionic - a complex anion in a complex compound K; neutral - the charge of the complex is 0. The complex compound of the outer sphere does not have, for example, . This is the formula for an anticancer drug.

4. According to the internal structure of the complex:

a) depending on the number of atoms of the complexing agent: mononuclear- the composition of the complex particle includes one atom of the complexing agent, for example Cl 3 ; multi-core- in the composition of the complex particle there are several atoms of the complexing agent - an iron-protein complex:

b) depending on the number of types of ligands, complexes are distinguished: homogeneous (single-ligand), containing one type of ligand, for example 2+, and heterogeneous (multi-ligand)- two kinds of ligands or more, for example Pt(NH 3) 2 Cl 2 . The complex includes NH 3 and Cl - ligands. For complex compounds containing different ligands in the inner sphere, geometric isomerism is characteristic, when, with the same composition of the inner sphere, the ligands in it are located differently relative to each other.

Geometric isomers of complex compounds differ not only in physical and chemical properties, but also in biological activity. The cis-isomer of Pt(NH 3) 2 Cl 2 has a pronounced antitumor activity, but the trans-isomer does not;

c) depending on the denticity of the ligands forming mononuclear complexes, the following groups can be distinguished:

Mononuclear complexes with monodentate ligands, for example 3+ ;

Mononuclear complexes with polydentate ligands. Complex compounds with polydentate ligands are called chelating compounds;

d) cyclic and acyclic forms of complex compounds.

7.8. CHELATE COMPLEXES. COMPLEXSONS. COMPLEXONATES

Cyclic structures that are formed as a result of the addition of a metal ion to two or more donor atoms belonging to one chelating agent molecule are called chelate compounds. For example, copper glycinate:

In them, the complexing agent, as it were, leads inside the ligand, is embraced by bonds, like claws, therefore, other things being equal, they are more stable than compounds that do not contain cycles. The most stable are cycles consisting of five or six links. This rule was first formulated by L.A. Chugaev. Difference

stability of the chelate complex and the stability of its non-cyclic analogue are called chelate effect.

Polydentate ligands that contain 2 types of groups act as a chelating agent:

1) groups capable of forming covalent polar bonds due to exchange reactions (proton donors, electron pair acceptors) -CH 2 COOH, -CH 2 PO (OH) 2, -CH 2 SO 2 OH, - acid groups (centers);

2) electron pair donor groups: ≡N, >NH, >C=O, -S-, -OH, - main groups (centers).

If such ligands saturate the inner coordination sphere of the complex and completely neutralize the charge of the metal ion, then the compounds are called intracomplex. For example, copper glycinate. There is no outer sphere in this complex.

A large group of organic substances containing basic and acid centers in the molecule is called complexones. These are polybasic acids. Chelate compounds formed by complexones when interacting with metal ions are called complexonates, for example, magnesium complexonate with ethylenediaminetetraacetic acid:

In aqueous solution, the complex exists in the anionic form.

Complexons and complexonates are a simple model of more complex compounds of living organisms: amino acids, polypeptides, proteins, nucleic acids, enzymes, vitamins and many other endogenous compounds.

Currently, a huge range of synthetic complexones with various functional groups is being produced. The formulas of the main complexones are presented below:

Complexons, under certain conditions, can provide unshared electron pairs (several) for the formation of a coordination bond with a metal ion (s-, p- or d-element). As a result, stable chelate-type compounds with 4-, 5-, 6-, or 8-membered rings are formed. The reaction proceeds over a wide pH range. Depending on pH, the nature of the complexing agent, its ratio with the ligand, complexonates of various strengths and solubility are formed. The chemistry of the formation of complexonates can be represented by equations using the sodium salt of EDTA (Na 2 H 2 Y) as an example, which dissociates in an aqueous solution: Na 2 H 2 Y → 2Na + + H 2 Y 2-, and the H 2 Y 2- ion interacts with ions metals, regardless of the degree of oxidation of the metal cation, most often one metal ion (1: 1) interacts with one complexone molecule. The reaction proceeds quantitatively (Kp>10 9).

Complexones and complexonates exhibit amphoteric properties in a wide pH range, the ability to participate in oxidation-reduction reactions, complex formation, form compounds with various properties depending on the degree of oxidation of the metal, its coordination saturation, and have electrophilic and nucleophilic properties. All this determines the ability to bind a huge number of particles, which allows a small amount of reagent to solve large and diverse problems.

Another indisputable advantage of complexones and complexonates is their low toxicity and the ability to convert toxic particles

into low-toxic or even biologically active ones. Decomposition products of complexonates do not accumulate in the body and are harmless. The third feature of complexonates is the possibility of their use as a source of trace elements.

Increased digestibility is due to the fact that the trace element is introduced in a biologically active form and has a high membrane permeability.

7.9. PHOSPHORUS-CONTAINING METAL COMPLEXONATES - AN EFFECTIVE FORM OF TRANSFORMATION OF MICRO AND MACRO ELEMENTS INTO A BIOLOGICALLY ACTIVE STATE AND A MODEL FOR STUDYING THE BIOLOGICAL ACTION OF CHEMICAL ELEMENTS

concept biological activity covers a wide range of phenomena. From the point of view of chemical impact, biologically active substances (BAS) are commonly understood as substances that can act on biological systems, regulating their vital activity.

The ability to such an impact is interpreted as the ability to exhibit biological activity. Regulation can manifest itself in the effects of stimulation, oppression, development of certain effects. The extreme manifestation of biological activity is biocidal action, when, as a result of the action of a biocide substance on the body, the latter dies. At lower concentrations, in most cases, biocides have a stimulating rather than lethal effect on living organisms.

A large number of such substances are currently known. Nevertheless, in many cases, the use of known biologically active substances is not used enough, often with an efficiency far from maximum, and the use often leads to side effects, which can be eliminated by introducing modifiers into biologically active substances.

Phosphorus-containing complexonates form compounds with various properties depending on the nature, degree of oxidation of the metal, coordination saturation, composition and structure of the hydrate shell. All this determines the multifunctionality of complexonates, their unique ability of substoichiometric action,

the effect of a common ion and provides wide application in medicine, biology, ecology and in various sectors of the national economy.

When the metal ion coordinates the complexon, the electron density is redistributed. Due to the participation of a lone electron pair in the donor-acceptor interaction, the electron density of the ligand (complexon) shifts to the central atom. A decrease in the relatively negative charge on the ligand contributes to a decrease in the Coulomb repulsion of the reagents. Therefore, the coordinated ligand becomes more accessible to attack by a nucleophilic reagent that has an excess of electron density on the reaction center. The shift of the electron density from the complexone to the metal ion leads to a relative increase in the positive charge of the carbon atom, and, consequently, to the facilitation of its attack by the nucleophilic reagent, the hydroxyl ion. Among the enzymes that catalyze metabolic processes in biological systems, the hydroxylated complex occupies one of the central places in the mechanism of enzymatic action and detoxification of the body. As a result of the multipoint interaction of the enzyme with the substrate, orientation occurs, which ensures the convergence of active groups in the active center and the transfer of the reaction to the intramolecular regime, before the reaction begins and the transition state is formed, which ensures the enzymatic function of FCM. Conformational changes can occur in enzyme molecules. Coordination creates additional conditions for the redox interaction between the central ion and the ligand, since a direct bond is established between the oxidizing agent and the reducing agent, which ensures the transfer of electrons. FCM transition metal complexes can be characterized by L-M, M-L, M-L-M type electron transitions, in which the orbitals of both the metal (M) and ligands (L) participate, which are respectively linked in the complex by donor-acceptor bonds. Complexons can serve as a bridge along which the electrons of multinuclear complexes oscillate between the central atoms of one or different elements in different oxidation states. (electron and proton transport complexes). Complexons determine the reducing properties of metal complexonates, which allows them to exhibit high antioxidant, adaptogenic properties, homeostatic functions.

So, complexones convert microelements into a biologically active, accessible form for the body. They form stable

more coordinatively saturated particles, incapable of destroying biocomplexes, and, consequently, low-toxic forms. Complexonates favorably act in violation of the microelement homeostasis of the body. Ions of transition elements in the complexonate form act in the body as a factor that determines the high sensitivity of cells to microelements through their participation in the creation of a high concentration gradient, the membrane potential. Transition metal complexonates FKM have bioregulatory properties.

The presence of acidic and basic centers in the composition of FCM provides amphoteric properties and their participation in maintaining acid-base balance (isohydric state).

With an increase in the number of phosphonic groups in the composition of the complexone, the composition and conditions for the formation of soluble and poorly soluble complexes change. An increase in the number of phosphonic groups favors the formation of sparingly soluble complexes in a wider pH range and shifts the area of ​​their existence to the acidic area. The decomposition of the complexes occurs at a pH of more than 9.

The study of the processes of complex formation with complexones made it possible to develop methods for the synthesis of bioregulators:

Growth stimulants of prolonged action in a colloid-chemical form are polynuclear homo- and heterocomplex compounds of titanium and iron;

Growth stimulants in water-soluble form. These are mixed-ligand titanium complexonates based on complexones and an inorganic ligand;

Growth inhibitors - phosphorus-containing complexonates of s-elements.

The biological effect of the synthesized drugs on growth and development was studied in a chronic experiment on plants, animals and humans.

Bioregulation- this is a new scientific direction that allows you to regulate the direction and intensity of biochemical processes, which can be widely used in medicine, animal husbandry and crop production. It is associated with the development of ways to restore the physiological function of the body in order to prevent and treat diseases and age-related pathologies. Complexones and complex compounds based on them can be classified as promising biologically active compounds. The study of their biological action in a chronic experiment showed that chemistry gave into the hands of physicians,

livestock breeders, agronomists and biologists, a new promising tool that allows you to actively influence a living cell, regulate nutritional conditions, growth and development of living organisms.

A study of the toxicity of the complexones and complexonates used showed the complete absence of the effect of drugs on the hematopoietic organs, blood pressure, excitability, respiratory rate: no change in liver function was noted, no toxicological effect on the morphology of tissues and organs was detected. Potassium salt of HEDP has no toxicity at a dose 5-10 times higher than the therapeutic one (10-20 mg/kg) in the study for 181 days. Therefore, complexones are classified as low-toxic compounds. They are used as medicines to combat viral diseases, poisoning by heavy metals and radioactive elements, calcium metabolism disorders, endemic diseases and microelement imbalance in the body. Phosphorus-containing complexons and complexonates do not undergo photolysis.

Progressive pollution of the environment with heavy metals - products of human economic activity is a permanent environmental factor. They can accumulate in the body. Excess and lack of them cause intoxication of the body.

Metal complexonates retain the chelating effect on the ligand (complexone) in the body and are indispensable for maintaining metal ligand homeostasis. Incorporated heavy metals are neutralized to a certain extent in the body, and low resorption capacity prevents the transfer of metals along trophic chains, as a result, this leads to a certain “biominization” of their toxic effect, which is especially important for the Ural region. For example, the free lead ion belongs to thiol poisons, and the strong complexonate of lead with ethylenediaminetetraacetic acid is of low toxicity. Therefore, detoxification of plants and animals consists in the use of metal complexonates. It is based on two thermodynamic principles: their ability to form strong bonds with toxic particles, turning them into poorly soluble or stable compounds in an aqueous solution; their inability to destroy endogenous biocomplexes. In this regard, we consider an important direction in the fight against eco-poisoning and obtaining environmentally friendly products - this is complex therapy of plants and animals.

A study was made of the effect of plant treatment with complexonates of various metals under intensive cultivation technology.

potatoes on the microelement composition of potato tubers. Tuber samples contained 105-116 mg/kg iron, 16-20 mg/kg manganese, 13-18 mg/kg copper and 11-15 mg/kg zinc. The ratio and content of microelements are typical for plant tissues. Tubers grown with and without the use of metal complexonates have almost the same elemental composition. The use of chelates does not create conditions for the accumulation of heavy metals in tubers. Complexonates, to a lesser extent than metal ions, are sorbed by the soil, are resistant to its microbiological effects, which allows them to be retained in the soil solution for a long time. The aftereffect is 3-4 years. They combine well with various pesticides. The metal in the complex has a lower toxicity. Phosphorus-containing metal complexonates do not irritate the mucous membrane of the eyes and do not damage the skin. Sensitizing properties have not been identified, the cumulative properties of titanium complexonates are not pronounced, and in some cases they are very weakly expressed. The cumulation coefficient is 0.9-3.0, which indicates a low potential danger of chronic drug poisoning.

Phosphorus-containing complexes are based on the phosphorus-carbon bond (C-P), which is also found in biological systems. It is part of the phosphonolipids, phosphonoglycans and phosphoproteins of cell membranes. Lipids containing aminophosphonic compounds are resistant to enzymatic hydrolysis, provide stability and, consequently, normal functioning of the outer cell membranes. Synthetic analogues of pyrophosphates - diphosphonates (Р-С-Р) or (Р-С-С-Р) in large doses disrupt calcium metabolism, and in small doses normalize it. Diphosphonates are effective in hyperlipemia and promising from the standpoint of pharmacology.

Diphosphonates containing P-C-P bonds are building blocks biosystems. They are biologically effective and are analogues of pyrophosphates. Diphosphonates have been shown to be effective in the treatment of various diseases. Diphosphonates are active inhibitors of bone mineralization and resorption. Complexons convert microelements into a biologically active form accessible to the body, form stable, more coordinatively saturated particles that are unable to destroy biocomplexes, and therefore, low-toxic forms. They determine the high sensitivity of cells to trace elements, participating in the formation of a high concentration gradient. Able to participate in the formation of polynuclear titanium compounds

of a different type - electron and proton transport complexes, participate in the bioregulation of metabolic processes, the body's resistance, the ability to form bonds with toxic particles, turning them into poorly soluble or soluble, stable, non-destructive endogenous complexes. Therefore, their use for detoxification, elimination from the body, obtaining environmentally friendly products (complex therapy), as well as in industry for the regeneration and disposal of industrial wastes of inorganic acids and transition metal salts is very promising.

7.10. LIGAND EXCHANGE AND METAL EXCHANGE

BALANCE. CHELATHERAPY

If there are several ligands with one metal ion or several metal ions with one ligand capable of forming complex compounds in the system, then competing processes are observed: in the first case, ligand-exchange equilibrium is competition between ligands for a metal ion, in the second case, metal-exchange equilibrium is competition between ions metal for the ligand. The process of formation of the most durable complex will prevail. For example, in solution there are ions: magnesium, zinc, iron (III), copper, chromium (II), iron (II) and manganese (II). When a small amount of ethylenediaminetetraacetic acid (EDTA) is introduced into this solution, competition between metal ions and binding to the iron (III) complex occur, since it forms the most stable complex with EDTA.

The interaction of biometals (Mb) and bioligands (Lb), the formation and destruction of vital biocomplexes (MbLb) are constantly taking place in the body:

In the body of humans, animals and plants, there are various mechanisms for protecting and maintaining this balance from various xenobiotics (foreign substances), including heavy metal ions. Ions of heavy metals that are not bound into a complex and their hydroxo complexes are toxic particles (Mt). In these cases, along with the natural metal ligand equilibrium, a new equilibrium may arise, with the formation of more stable foreign complexes containing toxicant metals (MtLb) or toxicant ligands (MbLt), which do not fulfill

essential biological functions. When exogenous toxic particles enter the body, combined equilibria arise and, as a result, competition of processes occurs. The predominant process will be the one that leads to the formation of the most stable complex compound:

Violations of metal ligand homeostasis cause metabolic disorders, inhibit the activity of enzymes, destroy important metabolites such as ATP, cell membranes, and disrupt the ion concentration gradient in cells. Therefore, artificial protection systems are being created. Chelation therapy (complex therapy) takes its due place in this method.

Chelation therapy is the removal of toxic particles from the body, based on their chelation with s-element complexonates. Drugs used to remove toxic particles incorporated in the body are called detoxifiers.(Lg). Chelation of toxic species with metal complexonates (Lg) converts toxic metal ions (Mt) into non-toxic (MtLg) bound forms suitable for isolation and membrane permeation, transport and elimination from the body. They retain a chelating effect in the body both for the ligand (complexon) and for the metal ion. This ensures the metal ligand homeostasis of the body. Therefore, the use of complexonates in medicine, animal husbandry, and crop production provides detoxification of the body.

The basic thermodynamic principles of chelation therapy can be formulated in two positions.

I. A detoxicant (Lg) must effectively bind toxicant ions (Mt, Lt), newly formed compounds (MtLg) must be stronger than those that existed in the body:

II. The detoxifier should not destroy vital complex compounds (MbLb); compounds that can be formed during the interaction of a detoxifier and biometal ions (MbLg) should be less strong than those existing in the body:

7.11. APPLICATION OF COMPLEXONS AND COMPLEXONATES IN MEDICINE

Complexone molecules practically do not undergo splitting or any change in the biological environment, which is their important pharmacological feature. Complexons are insoluble in lipids and highly soluble in water, so they do not penetrate or penetrate poorly through cell membranes, and therefore: 1) are not excreted by the intestines; 2) the absorption of complexing agents occurs only when they are injected (only penicillamine is taken orally); 3) in the body, complexons circulate mainly in the extracellular space; 4) excretion from the body is carried out mainly through the kidneys. This process is fast.

Substances that eliminate the effects of poisons on biological structures and inactivate poisons through chemical reactions are called antidotes.

One of the first antidotes to be used in chelation therapy is British Anti-Lewisite (BAL). Unithiol is currently used:

This drug effectively removes arsenic, mercury, chromium and bismuth from the body. The most widely used for poisoning with zinc, cadmium, lead and mercury are complexones and complexonates. Their use is based on the formation of stronger complexes with metal ions than complexes of the same ions with sulfur-containing groups of proteins, amino acids and carbohydrates. EDTA preparations are used to remove lead. The introduction of large doses of drugs into the body is dangerous, since they bind calcium ions, which leads to disruption of many functions. Therefore, apply tetacin(CaNa 2 EDTA), which is used to remove lead, cadmium, mercury, yttrium, cerium and other rare earth metals and cobalt.

Since the first therapeutic use of tetacin in 1952, this drug has found wide use in the clinic of occupational diseases and continues to be an indispensable antidote. The mechanism of action of tetacin is very interesting. Ions-toxicants displace the coordinated calcium ion from tetacin due to the formation of stronger bonds with oxygen and EDTA. The calcium ion, in turn, displaces the two remaining sodium ions:

Tetacin is introduced into the body in the form of a 5-10% solution, the basis of which is saline. So, already 1.5 hours after intraperitoneal injection, 15% of the administered dose of tetacin remains in the body, after 6 hours - 3%, and after 2 days - only 0.5%. The drug acts effectively and quickly when using the inhalation method of tetacin administration. It is rapidly absorbed and circulates in the blood for a long time. In addition, tetacin is used in protection against gas gangrene. It inhibits the action of zinc and cobalt ions, which are activators of the enzyme lecithinase, which is a gas gangrene toxin.

The binding of toxicants by tetacin into a low-toxic and more durable chelate complex, which is not destroyed and is easily excreted from the body through the kidneys, provides detoxification and balanced mineral nutrition. Close in structure and composition to pre-

paratam EDTA is the sodium-calcium salt of diethylenetriamine-pentaacetic acid (CaNa 3 DTPA) - pentacin and sodium salt of dacid (Na 6 DTPF) - trimefacin. Pentacin is used mainly for poisoning with compounds of iron, cadmium and lead, as well as for the removal of radionuclides (technetium, plutonium, uranium).

Sodium salt of ethyacid (СаNa 2 EDTP) phosphicin successfully used to remove mercury, lead, beryllium, manganese, actinides and other metals from the body. Complexonates are very effective in removing some toxic anions. For example, cobalt (II) ethylenediaminetetraacetate, which forms a mixed-ligand complex with CN - , can be recommended as an antidote for cyanide poisoning. A similar principle underlies methods for removing toxic organic substances, including pesticides containing functional groups with donor atoms capable of interacting with the complexonate metal.

An effective drug is succimer(dimercaptosuccinic acid, dimercaptosuccinic acid, chemet). It strongly binds almost all toxicants (Hg, As, Pb, Cd), but removes ions of biogenic elements (Cu, Fe, Zn, Co) from the body, so it is almost never used.

Phosphorus-containing complexonates are powerful inhibitors of crystal formation of phosphates and calcium oxalates. As an anticalcifying drug in the treatment of urolithiasis, ksidifon, a potassium-sodium salt of OEDP, is proposed. Diphosphonates, in addition, in minimal doses increase the incorporation of calcium into bone tissue, and prevent its pathological exit from the bones. HEDP and other diphosphonates prevent various types of osteoporosis, including renal osteodystrophy, periodontal

ny destruction, as well as the destruction of the transplanted bone in animals. The anti-atherosclerotic effect of HEDP has also been described.

In the USA, a number of diphosphonates, in particular HEDP, have been proposed as pharmaceutical preparations for the treatment of humans and animals suffering from metastasized bone cancer. By regulating membrane permeability, bisphosphonates promote the transport of antitumor drugs into the cell, and hence the effective treatment of various oncological diseases.

One of the current problems modern medicine is the task of rapid diagnosis of various diseases. In this aspect, of undoubted interest is a new class of preparations containing cations capable of performing the functions of a probe - radioactive magnetorelaxation and fluorescent labels. Radioisotopes of certain metals are used as the main components of radiopharmaceuticals. Chelation of the cations of these isotopes with complexones makes it possible to increase their toxicological acceptability for the body, to facilitate their transportation, and to ensure, within certain limits, the selectivity of concentration in various organs.

These examples by no means exhaust the whole variety of forms of application of complexonates in medicine. Thus, the dipotassium salt of magnesium ethylenediaminetetraacetate is used to regulate the fluid content in tissues in pathology. EDTA is used as part of anticoagulant suspensions used in the separation of blood plasma, as a stabilizer of adenosine triphosphate in the determination of blood glucose, in the clarification and storage of contact lenses. Diphosphonates are widely used in the treatment of rheumatoid diseases. They are especially effective as anti-arthritic agents in combination with anti-inflammatory agents.

7.12. COMPLEXES WITH MACROCYCLIC COMPOUNDS

Among natural complex compounds, a special place is occupied by macrocomplexes based on cyclic polypeptides containing internal cavities of certain sizes, in which there are several oxygen-containing groups capable of binding cations of those metals, including sodium and potassium, whose dimensions correspond to the dimensions of the cavity. Such substances, being in biological

Rice. 7.2. Complex of valinomycin with K+ ion

ical materials, provide transport of ions through membranes and therefore are called ionophores. For example, valinomycin transports a potassium ion across the membrane (Fig. 7.2).

With the help of another polypeptide - gramicidin A sodium cations are transported by the relay mechanism. This polypeptide is folded into a "tube", the inner surface of which is lined with oxygen-containing groups. The result is

a sufficiently long hydrophilic channel with a certain cross section corresponding to the size of the sodium ion. The sodium ion, entering the hydrophilic channel from one side, is transferred from one to the other oxygen groups, like a relay race through an ion-conducting channel.

Thus, a cyclic polypeptide molecule has an intramolecular cavity, into which a substrate of a certain size and geometry can enter according to the principle of a key and a lock. The cavity of such internal receptors is lined with active centers (endoreceptors). Depending on the nature of the metal ion, non-covalent interaction (electrostatic, hydrogen bonding, van der Waals forces) with alkali metals and covalent interaction with alkaline earth metals can occur. As a result of this, supramolecules- complex associates consisting of two or more particles held together by intermolecular forces.

The most common in living nature are tetradentate macrocycles - porphins and corrinoids close to them in structure. Schematically, the tetradent cycle can be represented in the following form (Fig. 7.3), where the arcs mean the same type of carbon chains connecting donor nitrogen atoms in a closed cycle; R 1 , R 2 , R 3 , P 4 are hydrocarbon radicals; M n+ - metal ion: in chlorophyll Mg 2+ ion, in hemoglobin Fe 2+ ion, in hemocyanin Cu 2+ ion, in vitamin B 12 (cobalamin) Co 3+ ion.

Donor nitrogen atoms are located at the corners of the square (indicated by the dotted line). They are tightly coordinated in space. So

porphyrins and corrinoids form strong complexes with cations of various elements and even alkaline earth metals. It is significant that Regardless of the denticity of the ligand, the chemical bond and structure of the complex are determined by donor atoms. For example, copper complexes with NH 3 , ethylenediamine, and porphyrin have the same square structure and a similar electronic configuration. But polydentate ligands bind to metal ions much more strongly than monodentate ligands.

Rice. 7.3. Tetradentate macrocycle

with the same donor atoms. The strength of ethylenediamine complexes is 8-10 orders of magnitude greater than the strength of the same metals with ammonia.

Bioinorganic complexes of metal ions with proteins are called bioclusters - complexes of metal ions with macrocyclic compounds (Fig. 7.4).

Rice. 7.4. Schematic representation of the structure of bioclusters of certain sizes of protein complexes with ions of d-elements. Types of interactions of a protein molecule. M n+ - active center metal ion

There is a cavity inside the biocluster. It includes a metal that interacts with donor atoms of the linking groups: OH - , SH - , COO - , -NH 2 , proteins, amino acids. The most famous metal-

ments (carbonic anhydrase, xanthine oxidase, cytochromes) are bioclusters whose cavities form enzyme centers containing Zn, Mo, Fe, respectively.

7.13. MULTICORE COMPLEXES

Heterovalent and heteronuclear complexes

Complexes, which include several central atoms of one or different elements, are called multi-core. The possibility of forming multinuclear complexes is determined by the ability of some ligands to bind to two or three metal ions. Such ligands are called bridge. Respectively bridge are called complexes. In principle, one-atom bridges are also possible, for example:

They use lone electron pairs belonging to the same atom. The role of bridges can be played polyatomic ligands. In such bridges, unshared electron pairs belonging to different atoms are used. polyatomic ligand.

A.A. Grinberg and F.M. Filinov studied bridging compounds of composition , in which the ligand binds complex compounds of the same metal, but in different oxidation states. G. Taube called them electron transfer complexes. He investigated the reactions of electron transfer between the central atoms of various metals. Systematic studies of the kinetics and mechanism of redox reactions have led to the conclusion that the transfer of an electron between two complexes is

proceeds through the resulting ligand bridge. The exchange of an electron between 2 + and 2 + occurs through the formation of an intermediate bridge complex (Fig. 7.5). Electron transfer occurs through the chloride bridging ligand, ending in the formation of 2+ complexes; 2+.

Rice. 7.5. Electron transfer in an intermediate multinuclear complex

A wide variety of polynuclear complexes has been obtained through the use of organic ligands containing several donor groups. The condition for their formation is such an arrangement of donor groups in the ligand that does not allow chelate cycles to close. It is not uncommon for a ligand to close the chelate cycle and simultaneously act as a bridge.

The active principle of electron transfer are transition metals that exhibit several stable oxidation states. This gives titanium, iron and copper ions ideal electron carrier properties. The set of options for the formation of heterovalent (HVA) and heteronuclear complexes (HNC) based on Ti and Fe is shown in Fig. . 7.6.

reaction

Reaction (1) is called cross reaction. In exchange reactions, the intermediate will be heterovalent complexes. All theoretically possible complexes are actually formed in solution under certain conditions, which is proved by various physicochemical studies.

Rice. 7.6. Formation of heterovalent complexes and heteronuclear complexes containing Ti and Fe

methods. For electron transfer to occur, the reactants must be in states close in energy. This requirement is called the Franck-Condon principle. Electron transfer can occur between atoms of the same transition element, which are in different degrees of HWC oxidation, or different HJC elements, the nature of the metal centers of which is different. These compounds can be defined as electron transport complexes. They are convenient carriers of electrons and protons in biological systems. The addition and release of an electron causes changes only in the electronic configuration of the metal, without changing the structure of the organic component of the complex. All these elements have several stable oxidation states (Ti +3 and +4; Fe +2 and +3; Cu +1 and +2). In our opinion, these systems are given by nature a unique role of ensuring the reversibility of biochemical processes with minimal energy costs. Reversible reactions include reactions that have thermodynamic and thermochemical constants from 10 -3 to 10 3 and with a small value of ΔG o and E o processes. Under these conditions, the initial substances and reaction products can be in comparable concentrations. When changing them in a certain range, it is easy to achieve the reversibility of the process, therefore, in biological systems, many processes are oscillatory (wave) in nature. Redox systems containing the above pairs cover a wide range of potentials, which allows them to enter into interactions accompanied by moderate changes in Δ Go and E°, with many substrates.

The probability of formation of HVA and HJA increases significantly when the solution contains potentially bridging ligands, i.e. molecules or ions (amino acids, hydroxy acids, complexones, etc.) capable of linking two metal centers at once. The possibility of delocalization of an electron in the HWC contributes to a decrease in the total energy of the complex.

More realistically, the set of possible options for the formation of HWC and HJA, in which the nature of the metal centers is different, is seen in Fig. 7.6. A detailed description of the formation of HVA and HNA and their role in biochemical systems are considered in the works of A.N. Glebova (1997). Redox pairs must structurally adjust to each other, then the transfer becomes possible. By selecting the components of the solution, one can "lengthen" the distance over which an electron is transferred from the reducing agent to the oxidizing agent. With a coordinated movement of particles, an electron can be transferred over long distances by the wave mechanism. As a "corridor" can be a hydrated protein chain, etc. The probability of electron transfer to a distance of up to 100A is high. The length of the "corridor" can be increased by additives (alkali metal ions, supporting electrolytes). This opens up great opportunities in the field of controlling the composition and properties of HWC and HJA. In solutions, they play the role of a kind of "black box" filled with electrons and protons. Depending on the circumstances, he can give them to other components or replenish his "reserves". The reversibility of reactions involving them makes it possible to repeatedly participate in cyclic processes. Electrons move from one metal center to another, oscillate between them. The complex molecule remains asymmetric and can take part in redox processes. HWC and HJAC are actively involved in oscillatory processes in biological media. This type of reaction is called oscillatory reactions. They are found in enzymatic catalysis, protein synthesis and other biochemical processes accompanying biological phenomena. These include periodic processes of cellular metabolism, waves of activity in the heart tissue, in brain tissue, and processes occurring at the level of ecological systems. An important stage of metabolism is the splitting of hydrogen from nutrients. In this case, hydrogen atoms pass into the ionic state, and the electrons separated from them enter the respiratory chain and give up their energy to the formation of ATP. As we have established, titanium complexonates are active carriers of not only electrons, but also protons. The ability of titanium ions to perform their role in the active center of enzymes such as catalases, peroxidases and cytochromes is determined by its high ability to complex formation, the formation of coordinated ion geometry, the formation of multinuclear HVA and HJA of various compositions and properties as a function of pH, the concentration of the transition element Ti and the organic component of the complex, their molar ratio. This ability is manifested in an increase in the selectivity of the complex

in relation to substrates, products of metabolic processes, activation of bonds in the complex (enzyme) and substrate through coordination and changes in the shape of the substrate in accordance with the steric requirements of the active center.

Electrochemical transformations in the body associated with the transfer of electrons are accompanied by a change in the degree of oxidation of particles and the appearance of a redox potential in solution. A large role in these transformations belongs to the multinuclear HVA and HNA complexes. They are active regulators of free radical processes, a system for the utilization of reactive oxygen species, hydrogen peroxide, oxidizing agents, radicals, and are involved in the oxidation of substrates, as well as in maintaining antioxidant homeostasis, in protecting the body from oxidative stress. Their enzymatic action on biosystems is similar to enzymes (cytochromes, superoxide dismutase, catalase, peroxidase, glutathione reductase, dehydrogenases). All this indicates high antioxidant properties of complexonates of transition elements.

7.14. QUESTIONS AND TASKS FOR SELF-CHECKING OF PREPAREDNESS FOR LESSONS AND EXAMS

1. Give the concept of complex compounds. How do they differ from double salts, and what do they have in common?

2. Make formulas of complex compounds according to their name: ammonium dihydroxotetrachloroplatinate (IV), triammintrinitrocobalt (III), give their characteristics; indicate the internal and external coordination sphere; the central ion and the degree of its oxidation: ligands, their number and denticity; the nature of the connections. Write the dissociation equation in an aqueous solution and the expression for the stability constant.

3. General properties of complex compounds, dissociation, stability of complexes, chemical properties of complexes.

4. How is the reactivity of complexes characterized from thermodynamic and kinetic positions?

5. Which amino complexes will be more durable than tetraamino-copper (II), and which ones will be less durable?

6. Give examples of macrocyclic complexes formed by alkali metal ions; d-element ions.

7. On what basis are complexes classified as chelated? Give examples of chelate and non-chelate complex compounds.

8. Using the example of copper glycinate, give the concept of intracomplex compounds. Write the structural formula of magnesium complexonate with ethylenediaminetetraacetic acid in sodium form.

9. Give a schematic structural fragment of any polynuclear complex.

10. Define polynuclear, heteronuclear and heterovalent complexes. The role of transition metals in their formation. Biological role component data.

11. What types of chemical bonds are found in complex compounds?

12. List the main types of hybridization of atomic orbitals that can occur at the central atom in the complex. What is the geometry of the complex depending on the type of hybridization?

13. Based on the electronic structure of the atoms of the elements of s-, p- and d-blocks, compare the ability to complex formation and their place in the chemistry of complexes.

14. Define complexones and complexonates. Give examples of the most used in biology and medicine. Give the thermodynamic principles on which chelation therapy is based. The use of complexonates for the neutralization and elimination of xenobiotics from the body.

15. Consider the main cases of violation of metal-ligand homeostasis in the human body.

16. Give examples of biocomplex compounds containing iron, cobalt, zinc.

17. Examples of competing processes involving hemoglobin.

18. The role of metal ions in enzymes.

19. Explain why for cobalt in complexes with complex ligands (polydentate) the oxidation state +3 is more stable, and in ordinary salts, such as halides, sulfates, nitrates, the oxidation state is +2?

20. For copper, oxidation states +1 and +2 are characteristic. Can copper catalyze electron transfer reactions?

21. Can zinc catalyze redox reactions?

22. What is the mechanism of action of mercury as a poison?

23. Indicate the acid and base in the reaction:

AgNO 3 + 2NH 3 \u003d NO 3.

24. Explain why the potassium-sodium salt of hydroxyethylidene diphosphonic acid, and not HEDP, is used as a drug.

25. How is the transport of electrons in the body carried out with the help of metal ions, which are part of biocomplex compounds?

7.15. TESTS

1. The oxidation state of the central atom in the complex ion is 2- is equal to:

a)-4;

b) +2;

in 2;

d) +4.

2. The most stable complex ion:

a) 2-, Kn = 8.5x10 -15;

b) 2-, Kn = 1.5x10 -30;

c) 2-, Kn = 4x10 -42;

d) 2-, Kn = 1x10 -21.

3. The solution contains 0.1 mol of the PtCl 4 4NH 3 compound. Reacting with AgNO 3 , it forms 0.2 mol of AgCl precipitate. Give the starting substance the coordination formula:

a)Cl;

b) Cl 3 ;

c) Cl 2 ;

d) Cl 4 .

4. What is the shape of the complexes formed as a result of sp 3 d 2-gi- breeding?

1) tetrahedron;

2) square;

4) trigonal bipyramid;

5) linear.

5. Choose the formula for the compound pentaamminechlorocobalt (III) sulfate:

a) Na 3 ;

6) [CoCl 2 (NH 3) 4 ]Cl;

c) K 2 [Co(SCN) 4];

d) SO 4 ;

e) [Co(H 2 O) 6 ] C1 3 .

6. What ligands are polydentate?

a) C1 -;

b) H 2 O;

c) ethylenediamine;

d) NH 3 ;

e) SCN - .

7. Complexing agents are:

a) electron pair donor atoms;

c) atoms- and ions-acceptors of electron pairs;

d) atoms- and ions-donors of electron pairs.

8. The elements with the least complexing ability are:

a)s; c) d;

b) p; d) f

9. Ligands are:

a) electron pair donor molecules;

b) ions-acceptors of electron pairs;

c) molecules- and ions-donors of electron pairs;

d) molecules- and ions-acceptors of electron pairs.

10. Communication in the internal coordination sphere of the complex:

a) covalent exchange;

b) covalent donor-acceptor;

c) ionic;

d) hydrogen.

11. The best complexing agent will be:

COMPLEXES, organic compounds containing N, S or P atoms capable of coordination, as well as carboxyl, phosphonic and other acidic groups and forming stable intra-complex compounds - chelates with metal cations. The term "complexons" was introduced in 1945 by the Swiss chemist G. Schwarzenbach to designate aminopolycarboxylic acids exhibiting the properties of polydentate ligands.

Complexones are colorless crystalline substances, as a rule, soluble in water, aqueous solutions of alkalis and acids, insoluble in ethanol and other organic solvents; dissociate in the range of pH 2-14. In aqueous solutions with cations of transition d- and f-elements, alkaline earth and some alkali metals, complexones form stable intra-complex compounds - complexonates (mono- and polynuclear, medium, acidic, hydroxocomplexonates, etc.). Complexonates contain several chelate cycles, which makes these compounds highly stable.

More than two hundred complexones with different properties are used to solve a wide range of practical problems. The complexing properties of complexones depend on the structure of their molecules. Thus, an increase in the number of methylene groups between N atoms in the alkylenediamine fragment >N(CH 2) n N< или между атомами N и кислотными группами снижает устойчивость комплексонатов многих металлов, кроме Pd(II), Cd(II), Cu(II), Hg(II) и Ag(I), то есть приводит к повышению избирательности комплексонов. На избирательность взаимодействия комплексонов с ионами металлов также влияет наличие в молекулах комплексонов объёмных заместителей и таких функциональных групп, как -ОН, -SH, -NH 2 , -РО 3 Н 2 , -AsO 3 Н 2 .

The most widely used complexones are nitrilotriacetic acid (complexone I), ethylenediaminetetraacetic acid (EDTA, complexone II) and its disodium salt (trilon B, complexone III), as well as diethylenetriaminepentaacetic acid, a number of phosphoryl-containing complexones - nitrilotrimethylenephosphonic acid, ethylenacid, hydroxyethylidene diphosphonic acid. Phosphoryl-containing complexones form complexonates in a wide range of pH values, including in strongly acidic and strongly alkaline media; their complexonates with Fe(III), Al(III), and Be(II) are insoluble in water.

Complexons are used in the oil and gas industry to inhibit scaling during joint production, field gathering, transportation and preparation of oil of different grades, in the process of drilling and casing oil and gas wells. Complexons are used as titrants in complexometry in the determination of ions of many metals, as well as reagents for the separation and isolation of metals, water softeners, to prevent the formation (and dissolution) of deposits (for example, with increased water hardness) on the surface of heating equipment, as additives , slowing down the hardening of cement and gypsum, food and cosmetic stabilizers, components of detergents, fixatives in photography, electrolytes (instead of cyanide) in electroplating.

Complexones and complexonates, as a rule, are non-toxic and are quickly excreted from the body. In combination with the high complexing ability of complexones, this ensured the use of complexones and complexonates of some metals in agriculture for the prevention and treatment of anemia in animals (eg mink, piglets, calves) and plant chlorosis (mainly grapes, citrus and fruit crops). In medicine, complexones are used to remove toxic and radioactive metals from the body in case of poisoning by them, as regulators of calcium metabolism in the body, in oncology, in the treatment of certain allergic diseases, and in diagnostics.

Lit .: Plibil R. Complexons in chemical analysis. 2nd ed. M., 1960; Schwarzenbach G., Flashka G. Complexometric titration. M., 1970; Moskvin V. D. et al. The use of complexones in the oil industry // Journal of the All-Russian Chemical Society named after D. I. Mendeleev. 1984. V. 29. No. 3; Gorelov IP et al. Complexones - derivatives of dicarboxylic acids // Chemistry in agriculture. 1987. No. 1; Dyatlova N. M., Temkina V. Ya., Popov K. I. Complexons and complexonates of metals. M., 1988; Gorelov I.P. et al. Iminodisuccinic acid as a hydration retarder of a lime binder // Building materials. 2004. No. 5.