ABSTRACT:The effective crystal field (ECF) methodology previously developed for description of the electronic structure of transition metal complexes (TMCs) is combined with molecular mechanics (MM) formalism. In this way, a new method for calculations of potential energy surfaces of the Werner-type TMC is developed. It is based on a combined quantum mechanics (QM)-MM approach with the ECF method taking part of the QM and advanced MM package MMPC developed for the metal ion complex computations and based on the CHARMM organic force field. The MM region consists of ligand atoms and metal ion coordination sphere, leaving out effects of d-shell, while the QM region is limited to metal ion d-shell. Crystal field matrix for the d-shell is calculated with use of the local ECF method. It is shown that the procedure proposed reproduces with considerable accuracy geometry characteristics of values of the Fe(II) complexes with both mono-and polydentate ligands.

ABSTRACT:A version of molecular mechanics based on the Gillespie-Kepert model of coordination bonds "repulsion" is applied to lanthanide complexes. The force field parameters are developed that describe the structure of β-diketonate-, aqua-, and mixed aqua-β-diketonate complexes with good accuracy; the same parameters are applicable to various coordination numbers/polyhedra. For the aqua complexes, typical root-mean-square deviation (calculated vs. X-ray experimental values) is 0.02 Å in Ln-O bond lengths and 2.0• in O-Ln-O valence angles. For most of the other compounds, the same precision is achieved in coordination bond lengths, while 3.5• is a typical precision for coordination bond angles. Calculations successfully reproduce the puckering of the β-diketonate chelate rings, as well as the relative stability of isomers for a representative example.