(η-X)2[(μ-S2)M2] complex cores (X = O, S; M = MoV, WV): the syn/anti isomerism revisited by means of DFT calculations

Abstract

Abstract A series of five sulfur-rich binuclear, di-anionic complexes involving the (η-X)2[(μ-S2)M2] core (X = O, S; M = MoV, WV), and completed with two dithiolene ligands, is investigated by means of Density Functional Theory (DFT). Geometries have been optimized, in order to address the problem of the syn/anti isomerism. It is found that the equilibrium geometry of all investigated systems in either conformation deviates from the expected full symmetry. This distortion, mainly affecting the dithiolene ligands, is assigned to the strong electrostatic and Pauli repulsion, which develops inside the coordination sphere of each metal. These repulsive interactions are shown to be of similar strength in the syn and anti forms of the isolated molecules and do not critically affect the energy balance between the two isomers. As suggested 23 years ago by Chandler, Lichtenberger and Enemark (CLE), the bent σ bond provides the syn form a slight advantage (1–4 kcal mol–1) over the lateral σ bond characteristic of the anti isomer. It is expected that environmental effects and more specifically the location of the counterions are of crucial importance regarding the relief of the intramolecular repulsion and the relative stability of isomers in the crystal. To cite this article: M.-M. Rohmer et M. Benard,C. R. Chimie 8 (2005).