Trigonal prismatic coordination in tris(dithiolene) complexes: Guilty or just non-innocent?

The discovery of trigonal prismatic (TP) coordination in tris(dithiolene) complexes is recounted. The research was stimulated by the efforts of Gray, Schrauzer, Holm and Davison in the 1960s on the chemistry of dithiolene complexes that showed multiple reversible electron transfer processes and challenged conventional oxidation state assignments. The structures of Re(S(2)C(2)Ph(2))(3), V(S(2)C(2)Ph(2))(3) and Mo(S(2)C(2)H(2))(3) were reported at that time. Bonding pictures based on semiempirical molecular orbital calculations were presented and the basis for stability of TP coordination was put forward based on partial oxidation of the unsaturated 1,2-dithiolate ligands. The structures of M(L)(3)(n) complexes for M = Groups 5-7 and n = 0, -1, -2, -3 from the Cambridge structural database are tabulated. The results show that for any M(L)(3) system as the magnitude of n increases, the coordination geometry twists to intermediate between TP and octahedral. The notion of redox-non-innocence in the dithiolene ligands is revisited through the recent work of Wieghardt including two studies that focus on the molecular and electronic structures of Re(L)(3)(n) and V(L)(3)(n) complexes. New experimental work is briefly summarized and the bonding in these systems is reanalyzed. A comparison is given between the early studies of the 1960s and the experimentally and computationally more complete studies recently published (C) 2010 Elsevier B.V. All rights reserved.