Estimation of stability constants of copper(II) chelates with triamines and their mixed complexes with amino acids by using topological indices and the overlapping spheres method

Irving-Williams order in the framework of connectivity index ³χv enables simultaneous prediction of stability constants of bivalent transition metal complexes

Logarithms of stability constants, log K₁ and log β₂, of the first transition series metal mono- and bis-complexes with any of four aliphatic amino acids (glycine, alanine, valine and leucine) decrease monotonously with third order valence connectivity index, ³χ^v, from Cu²⁺ to Mn²⁺. While stability of the complexes with the same metal is linearly dependent on ³χ^v, stability constants of Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺complexes with the same ligand show a quadratic dependence on ³χ^v. As Cu²⁺ complexes deviate significantly from quadratic functions, models for the simultaneous estimation of the stability constants, yielding r = 0.999 (S.E. = 0.05) and r = 0.998 (S.E. = 0.11), for log K₁ and log β₂, respectively, were developed only for Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺ complexes with amino acids.