The formation constants of the complexes of the type [CuAL], where A=2,2′-bipyridyl, 1,10-phenanthroline, 2-(2′-pyridyl)benzimidazole, or 2-(2′-pyridyl)imidazoline and L=a dianion of catechol, tiron, protocatechuic acid, pyrogallol, 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, dopamine, or adrenaline, have been determined in a dioxan-water (1∶1, v/v) medium and μ=0·2 mol dm⁻³ NaClO₄ at 30°C, usingscogs method. The effect of the π acid character of A and substitution on ligand L on the ternary complex stability have been discussed.

The formation constants of the complexes of the type [NiAL], where A=2,2′-bipyridyl, 1,10-phenanthroline, 2-(2′-pyridyl) benzimidazole, or 2-(2′-pyridyl) imidazoline and L=ethylenediamine, 1,2-diaminopropane, N-methyl-ethylenediamine, glycine, α-alanine, β-alanine, malonate, histidine, or histamine have been determined in dioxan-water (1∶1 v/v) medium and μ=0·2 mol dm⁻³ NaClO₄ at 30°C. The values of ΔlogK_M (logK_MAL^MA−logK_ML^M) in Ni(II) complexes have been compared with corresponding Cu(II) complexes. It is observed that for [NiAL] complexes, where L=L¹ to L⁷, ΔlogK is more negative than for the corresponding [CuAL] complexes whereas in cases where L=L⁸, or L⁹, ΔlogK for Ni(II) complexes is less negative than for the corresponding Cu(II) complexes. The reason has been discussed.

The stability constants of ternary M(II) complexes, [MLL′], where M refers to Cu(II) or Ni(II), L refers to ethylenediamine (en), 1,3-diaminopropane (1,3-pn), N,N-dimethylethylenediamine (N,N-dimen), N,N-diethylethylenediamine (N,N-dien) and L′ refers to catechol, catechuic acid, tiron, pyrogallol,o-aminophenol,o-phenylenediamine, oxalic acid, malonic acid, glycine, α-alanine, β-alanine, have been determined potentiometrically using the SCOGS computer program. LogK_reprop. (reprop.-reproportionation) of ternary complexes have been calculated. The effecf of the nature of the ligand onK_reprop. values has been discussed for these ternary complexes and the fact thatK_reprop. is not a proper measure of the stability of the ternary complex has been indicated.