Complexes of heterocyclic thionates .1. Complexes of monodentate and chelating ligands

The monodentate and chelating behaviour of deprotonated heterocyclic thiones, otherwise known as the heterocyclic thionates, with transition and other metals is reported. The range of ligands involved is large and includes pyrimidine, imidazole, triazole: quinoline, purine, thiazole, thiadiazole and oxazole molecules, mostly as their monothionate derivatives. Some dithionate derivatives of mostly pyrimidine, quinoxaline and thiadiazole are also included. The preparation, spectroscopy and, in some cases, the electrochemical properties of the complexes are described. The review emphasizes the resultant geometries and dimensions derived from the crystal structures of the complexes contained in almost 180 references. Heterocyclic thionates are ambidentate monodentate ligands. They are sulphur donating towards organomercury(II) and aurophosphine(I) cations with supplementary intramolecular attachments to the thioamido nitrogen atoms in many cases. The alternative monodentate nitrogen-donating behaviour is mostly limited to zinc(II) complexes of benzo-1,3-thiazoline-2-thionate. Monosubstituted heterocyclic thionates are S,N-chelating and mostly generate four-membered rings. Some quinoline thionate derivatives are also S,N-chelating and generate five-membered rings, The dithionate derivatives are generally S,S-chelating and also generate five-membered rings. The complexes are mostly mononuclear with coordination at the metal ranging from two, for monodentate ligands, to eight for tetrachelates. The effect of deprotonation and coordination on the dimensions of parent heterocyclic thiones, especially those of pyridine-2-thione and benzo-1,3-thiazoline-2-thione, are also reported and discussed.