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 chemically active groups, –N(H)–C(=S)– left right arrow–N=C(–SH)– ,and are useful model compounds for sulphur-containing analogues of purine and pyrimidine bases. Heterocylic-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 binding, 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), silver(I) and mercury(II) is briefly described. As regards thiosemicarbazones, focus is only on two compounds, namely organomercury(II) and organothallium(III). A variety of new molecules, well characterised by NMR and X-ray crystallography, is introduced.