Deriving a Mechanistic Model for Potential Energy Surface of Coordination Compounds of Nontransition Elements

Molecules of coordination compounds (those formed by a central atom—largely by a transition or non-transition metal ion, but also by non-transition elements like sulfur, phosphorus, etc., and by atoms or groups surrounding it—the ligands) for decades represent a significant problem for any “classical” description given in terms of empirical force fields of molecular mechanics (MM) due to diversity of coordination polyhedra resulting in the numerosity of the parameters necessary to describe the objects of interest within such a setting. This situation is further toughened by the specific collection of effects known as mutual influence of ligands, of which the trans-effect in transition metal complexes is the most known. A feature particularly complicating understanding the ligand influence is its qualitative dependence on the nature of the central atom. The real source of these problems is of course the specificity of the electronic structure of the coordination compounds. If compared with usual organic molecules for which the MM in its classical form is rather successful the major distinction characteristic for coordination compounds is the absence of fairly distinguishable two-center two-electron bonds incident to its central atom (ion). Using a methodology called deductive molecular mechanics (DMM) we have recently shown that for “organic” molecules it is possible to sequentially derive the form of the MM force field departing from a simple but intuitively transparent model of electronic structure of a single chemical bond. Here we present an analogous derivation for the Correspondence to: A. L. Tchougréeff; e-mail: [email protected].