COMPLEXES OF HETEROCYCLIC THIONATES .1. COMPLEXES OF MONODENTATE AND CHELATING LIGANDS

The monodentate and chelating behaviour of deprotonated heterocyclic t hiones, 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, thiaz ole, thiadiazole and oxazole molecules, mostly as their monothionate d erivatives. Some dithionate derivatives of mostly pyrimidine, quinoxal ine and thiadiazole are also included. The preparation, spectroscopy a nd, in some cases, the electrochemical properties of the complexes are described. The review emphasizes the resultant geometries and dimensi ons derived from the crystal structures of the complexes contained in almost 180 references. Heterocyclic thionates are ambidentate monodent ate ligands. They are sulphur donating towards organomercury(II) and a urophosphine(I) cations with supplementary intramolecular attachments to the thioamido nitrogen atoms in many cases. The alternative monoden tate nitrogen-donating behaviour is mostly limited to zinc(II) complex es of benzo-1,3-thiazoline-2-thionate. Monosubstituted heterocyclic th ionates are S,N-chelating and mostly generate four-membered rings. Som e quinoline thionate derivatives are also S,N-chelating and generate f ive-membered rings, The dithionate derivatives are generally S,S-chela ting and also generate five-membered rings. The complexes are mostly m ononuclear with coordination at the metal ranging from two, for monode ntate ligands, to eight for tetrachelates. The effect of deprotonation and coordination on the dimensions of parent heterocyclic thiones, es pecially those of pyridine-2-thione and benzo-1,3-thiazoline-2-thione, are also reported and discussed.