Stereochemical trends of metal derivatives of some heterocyclic-2-thiones and thiosemicarbazones

The interaction of heterocyclic thiones/thiosemicarbazones with metals has been the subject of several investigations as these ligands contain chemica lly active groups, -N(H)-C(=S)- <----> -N=C(-SH)-,and are useful model comp ounds for sulphur-containing analogues of purine and pyrimidine bases. Hete rocylic-2-thiones bind to metals in several ways and lead to the formation of monomeric or polymeric complexes. For example, the simplest prototype of heterocylic-2-thiones, namely, pyridine-2-thione has several ways of bindi ng, notably, terminal S-bonding and S-bridging (in neutral form), while in anionic form the modes are terminal S-bonding, S-bridging, N,S-chelation, N ,S-bridging, N,S-chelation-cum-S-bridging and N,S-bridging-cum-S-bridging. Similarly, thiosemicarbazones bind to metals as S-bonded unidentates or N,S -chelates. In this paper, the chemistry of pyridine-2- thione, its N-oxide, 2-(benzylthio)pyridine-1-oxide thione with metals like iron(II), ruthenium (II), nickel(II), palladium(II), platinum(II), copper(I), copper(II), silve r(I) and mercury(II) is briefly described. As regards thiosemicarbazones, f ocus is only on two compounds, namely organomercury(II) and organothallium( III). A variety of new molecules, well characterised by NMR and X-ray cryst allography, is introduced.