Complexes of heterocyclic thionates Part 2: complexes of bridging ligands

Abstract

The bridging behaviour of deprotonated heterocyclic thiones, the heterocyclic thionates, is reported. The anions are effective bridging ligands among binuclear, trinuclear, tetranuclear hexanuclear and polynuclear metallic species. The metals involved are mostly from the second and third series of transition metals together with some from the first transition series. Some examples involving main group metals are also included. The anionic ligands included in the review mostly involve the monothionate derivatives of pyridine, imidazole, triazole, quinoline, thiazole, and thiadiazole derivatives. Dithionate derivatives are few in number and are limited to μ 2-S,N bridging pyrimidine and μ 2-S,S bridging 1,2,5-thiadiazole bases. Several bridging modes are described. These may involve the exclusive use of the thionate sulphur atom in the rare edge-bridging, μ 2-S( η 2-S), of two metal centres. Alternatively, both the sulphur and the nitrogen atoms of the thioamide groups may be involved in the formation of either binuclear double-bridging, μ 2-( η 1-S; η 1-N), or binuclear triple-bridgng, μ 2-( η 2-S; η 1-N) systems. Trinuclear face-briding, μ 3-( η 2-S; η 1-N), ligands occur among trinuclear, tetranuclear and octahedral complexes. Relatively rare tetranuclear, μ 4 ( η 3-S; η 1-N), bridging ligands generate polymeric and oligomeric complexes. Combinations of similar, or different, bridging arrangements are also involved in the formation of double or multiple bridges among binuclear and polynuclear metal centres. Preparative routes, vibrational and electronic spectra as well as the electrochemistry of the complexes are described and discussed. Isomeric forms of the complexes, arising mostly from a combination of the bifunctional and polydentate character of the bridging ligands towards the metal centres, are also described and discussed. The review emphasises the structures and dimensions derived from the X-ray crystallographic study of a large number of binuclear and polynuclear complexes. The effect of deprotonation and coordination on the dimensions of some of the parent ligands is also reported and discussed. Some structures, as well as some structural changes, derived from solution NMR spectra, are also reported.