Irving-Williams Order in the Framework of Connectivity Index 3χv Enables Simultaneous Prediction of Stability Constants of Bivalent Transition Metal Complexes

Ante Miličević,Gina Branica,Nenad Raos

doi:10.3390/molecules16021103

Ante Miličević, Gina Branica + Show 1 more

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https://doi.org/10.3390/molecules16021103

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Abstract

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, 3χv, from Cu2+ to Mn2+. While stability of the complexes with the same metal is linearly dependent on 3χv, stability constants of Mn2+, Fe2+, Co2+, and Ni2+complexes with the same ligand show a quadratic dependence on 3χv. 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.

Highlights

The Irving-Williams order of stability of bivalent transition metal complexes (Mn2+
Cannon developed an interpolation formula [3] to predict stability constants of chromium(II) complexes from the constants of copper(II), manganese(II), Molecules 2011, 16 and zinc(II), but it was later found to be in no way better than similar formulas based on one variable, namely stability constants of copper(II), or merely protonation constant of the ligand [4]
In our systematic attempt to develop regression models based on the third order valence connectivity index (3χv) for the prediction of stability constants of coordination compounds [5,6], we were concerned mostly with the copper(II) and nickel(II) chelates