Rhodium(III) complexes with pyridine-2-thiol (pySH) and pyridine-2-thiolato (pyS) as the only ligands: crystal structures of mer-[Rh(pyS)3], [Rh(pyS)2(pySH)2]Cl·0.5H2O, and [Rh(pyS)3(pySH)]

Abstract

The rhodium(I) compound [Rh₂Cl₂(CO)₄] reacts with an excess of pyridine-2-thiol (pySH) in air to give orange crystals of the oxidised product [Rh(pyS)₂(pySH)₂]Cl, the single-crystal X-ray structure of which shows two chelating ligands pyS^– in an equatorial plane with mutually cis sulphur atoms. The monodentate neutral ligands (pySH) are trans co-ordinated through sulphur and are linked through NH ⋯ Cl^–⋯ HN hydrogen bonds to form a large pseudo-chelate ring. The neutral red compound [Rh(pyS)₃(pySH)] is formed only slowly following rapid deprotonation of the cation by basic alumina or NEt₃. The X-ray structure shows that a gross stereochemical change has occurred so that two monodentate ligands (pySH and pyS^–) are cis while the two chelating ligands (pyS^–) have mutually trans sulphur atoms. The deprotonation, with its associated stereochemical change, is reversible. The action of heat on [Rh(pyS)₃(pySH)] gives free pySH and mer-[Rh(pyS)₃](X-ray structure reported), which may also be obtained directly from RhCl₃·3H₂O and pySH in the presence of base.