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 K-1 and log beta(2), 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, (3)chi(v), from Cu2+ to Mn2+. While stability of the complexes with the same metal is linearly dependent on (3)chi(v), stability constants of Mn2+, Fe2+, Co2+, and Ni2+ complexes with the same ligand show a quadratic dependence on (3)chi(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 K-1 and log beta(2), respectively, were developed only for Mn2+, Fe2+, Co2+, and Ni2+ complexes with amino acids.