Procedure for the analysis of interfragment donor-acceptor interactions in transition metal complexes

The procedure based on the first order density matrix has been suggested for the description of molecular electronic structures. The procedure includes: The calculation of interatomic bond-order indices and their ??-, ??-, and ??-components; the construction of multicenter orbitals localized on fragments responsible for the formation of bonds inside fragments and between fragments; the classification of the constructed orbitals according to their population, valence activity, and orientation; the characterization of the realized donoracceptor abilities of the fragments (ligands and more complicated structural units). The interaction between fragments is described by a rather small number of multicenter orbitals localized on them. The concept of the valence activity of a polyatomic fragment has been introduced and the algorithm of its calculation has been offered. The procedure is illustrated by the analysis of electronic structures of ruthenium(II), platinum(II), and rhodium(I) complexes.