Mixed-ligand nickel( ii ) and copper( ii ) complexes in competitive chelation reactions with polyaminopolyacetate and po
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Mixed-ligand nickel(II) and copper(II) complexes in competitive chelation reactions with polyaminopolyacetate and polyamine ligands* N. V. Scheglovaa and T. V. Popovab aMari
State University, 1 pl. Lenina, 424000 Yoshkar-Ola, Russian Federation. Fax: +7 (836 2) 64 1541. E-mail: [email protected] bState University of Humanities and Technology, 22 Zelenaya ul., 142611 Orekhovo-Zuevo, Russian Federation. Fax: +7 (496) 425 7882. E-mail: [email protected] The mixed-ligand and competitive formation of coordination compounds in aqueous solutions of ternary systems containing nickel(II) or copper(II) cations, polyaminopolyacetate (nitrilotriacetic, ethylenediaminetetraacetic, or diethylenetriaminepentaacetic acid), and polyamine (ethylenediamine, diethylenetriamine, or triethylenetetramine) ligands was studied by spectrophotometry. The factors were determined which facilitate the formation of mixed-ligand complexes of composition [ML1L2] (M is NiII or CuII, L1 is a polyaminopolyacetate chelating agent, L2 is a polyamine ligand) in aqueous solutions. In these complexes, amines act predominantly as polydentate chelating ligands and the coordination sphere of metal atoms is completed by nitrogen and oxygen atoms of the chelating agents. An increase in the denticity of the polyamine ligand was found to increase the number of ethylenediamine metallocycles and promote partial cleavage of glycinate rings of carboxylate ligands in the coordination polyhedron of the chelate, thereby providing an increase in the stability of the resulting mixed-ligand complex species. In systems containing copper(II) cations, the ability of polyamine ligands to exhibit a discriminatory effect and block the coordination of the polyaminopolyacetate chelating ligand was shown to vary and depend on the combination of L1 and L2 ligands in the coordination sphere. Key words: spectrophotometric method, mixed-ligand complexes, nickel(II), copper(II), competitive complexation.
The formation of mixed-ligand complexes is an area of extensive research in modern coordination chemistry. The goals of these studies are to reveal general patterns of the competitive ligand exchange in multicomponent solutions, determine the compatibility of complexing agents with increasing complexity of the composition of the complexes, and investigate the effects of the geometric, steric, and electrostatic factors on stability and properties of the resulting coordination species. The synthesis of complexes simultaneously containing different ligands, the determination of their stability, structures, and properties, and the establishment of relationships between thermodynamic or kinetic characteristics of the resulting mixed-ligand coordination species and parameters of the medium have attracted considerable attention because of a significant potential for the use of such complexes, including for the improvement of the compositions of work* Based on the materials of the XXI Mendeleev Congress on General and Applied Chemistry (September 9—13, 2019, St. Petersburg, Russia).
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