Equilibrium Studies on Copper(II) Ternary Complexes Containing <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-Asparagine & Some Potentially Tridentate Ligands

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Polarographic and potentiometric studies on some binary and ternary complex systems of dioxouranium(VI)

201-205The relative coordinating abilities of donor sites in the potentially tridentate ligands viz., asparagine. glutamine, aspartic acid and glutamic acid towards uranyl ion have been invgestigated by polarographic and pH-metric techniques. The metal ion forms 1:2 complexes under polarographic conditions. However, only 1:1 complex is observed under pH-metric conditions, where 1:2 complexes do not proceed due to extensive hydrolysis of the metal ion. The relative variations of E1/2 with pH and ligand concentration supported by conductometric titration.data indicate that the primary amino groups in the amino acids are not involved in coordination with uranyl ion. Further, the amide groups in asparagine and glutamine also do not participate in coordination thus rendering these ligands unidentate, In aspartic and glutamic acid complexes, seven- and eight- membered chelate rings are formed involving two terminal carboxyl groups. The mixed ligand complex equilibria of uranyl ion involving aspartic acid/glutamic acid as primary ligands (A) and maleic acid, malonic acid, succinic acid and lactic acid as secondary ligands (B) have also been studied by computer based numerical evaluation of pH titration data. The concentration profiles have indicated the favourability of the formation of ternary complexes in general as reflected in the logK values

Effect of nickel(II) ternary complex formation on the coordination behaviour of glycylglycine in aqueous solution

576-579The stability constants of parent complexes of the ligands glycylglycine and glycinamide(A) with Ni(Il). and of the ternary complexes formed with Iigands imidazole, histamine and L-histidine(B) have been determined by the pH-metric measurements at 37°C and l = 0.15 mol dm- 3 (NaCIO4). It has been found that the ligands A form NiABH, NiAB, and NiAH-1 B mixed ligand complexes with histamine and -histidine(B) Iigands. while with imidazole(B) ligand the saturated NiA B2 and unsaturated NiAB species have been found to be present. The mode of coordination of ligands A and B in the NiABH and NiAB/NiAB2 ternary species is similar to their binding in their respective binary species. Though amide deprotonated glycylglycine is tridentate in its NiAH-1 species, in the NiAH -1B ternary species in the Ni(II)-glycylglycine(A)-histamine/-histidine(B) systems. it binds the metal in a bidentate manner