COMPLEXES OF HETEROCYCLIC THIONATES .2. COMPLEXES OF BRIDGING LIGANDS

The bridging behaviour of deprotonated heterocyclic thiones, the heter ocyclic thionates, is reported. The anions are effective bridging liga nds among binuclear, trinuclear, tetranuclear, hexanuclear and polynuc lear metallic species. The metals involved are mostly from the second and third series of transition metals together with some from the firs t transition series. Some examples involving main group metals are als o included. The anionic ligands included in the review mostly involve the monothionate derivatives of pyridine, imidazole, triazole, quinoli ne, thiazole, and thiadiazole derivatives. Dithionate derivatives are few in number and are limited to mu(2)-S,N bridging pyrimidine and mu( 2)-S,S bridging 1,2,4-thiadiazole bases. Several bridging modes are de scribed. These may involve the exclusive use of the thionate sulphur a tom in the rare edge-bridging, mu(2)-S(eta(2)-S), of two metal centres . Alternatively, both the sulphur and the nitrogen atoms of the thioam ide groups may be involved in the formation of either binuclear double -bridging, mu(2)-(eta(1)-S;eta(1)-N), or binuclear triple-bridging, mu (2)(eta(2)-S;eta(1)-N) systems. Trinuclear face-bridging, mu(3)-(eta(2 )-S;eta(1)-N), ligands occur among trinuclear, tetranuclear and octahe dral complexes. Relatively rare tetranuclear, mu(4)(eta(3)-S;eta(1)-N) , bridging ligands generate polymeric and oligomeric complexes. Combin ations of similar, or different, bridging arrangements are also involv ed in the formation of double or multiple bridges among binuclear and polynuclear metal centres. Preparative routes, vibrational and electro nic spectra as well as the electrochemistry of the complexes are descr ibed and discussed. Isomeric forms of the complexes, arising mostly fr om a combination of the bifunctional and polydentate character of the bridging ligands towards the metal centres, are also described and dis cussed. The review emphasises the structures and dimensions derived fr om the X-ray crystallographic study of a large number of binuclear and polynuclear complexes. The effect of deprotonation and coordination o n the dimensions of some of the parent ligands is also reported and di scussed. Some structures, as well as some structural changes, derived from solution NMR spectra, are also reported. (C) 1997 Elsevier Scienc e S.A.