New materials based on metal complexes of sulphur donor ligands
A comparative account is given of the stuctures and properties of the complexes of the type N(M(mnt)2)( where N is a monovalent cation, M is Ni, Pd or Pt and mnt is C&S2) together with the recently discovered new lowdimensional metal Cs(Pd(amit)2)2(where dmit is C3S5). Metal complexes of sulphur donor ligands have been widely studied, often because their intense c olours made them useful in analysis. In the 1960's studies on metal complexes of ligands such as the dithiolenes centred on their unusual redox Properties (ref. 1). More recently it has been found that they exhibit a wide range of structures and properties in the solid state dependent upon the nature and extent of the interactions between the metal-complex anions (refs. 2-7). Extensive studies have been made of the complexes formed between the ligands l,Z-dicyanoethylene-l,2dithiol( (HS)zCz( CN)z, HZmnt ) and 4,5-dimercapto-1, a-dithiole-2-thione (dmit) and nickel( I1 ), palladium( 11) and platinum( I1 ) salts, The resulting complex anions are planar and can readily exist either as the mono- or di-anion. The di-anion contains a pair of electrons in the HOMO and therefore inter-anion interactions in the solid state are extremely unlikely. The mono-anion, however, possesses a single e lectron in the HOMO, and therefore inter-anion interactions due to overlap of the HOMOS on adjacent anions are possible. The occurrence and the nature of these interactions is found to be very dependent on the central metal involved and the size of the cation. Thus the resulting complex can be a diamagnetic semiconductor or insulator, a semiconductor exhibiting a magnetic transition or a lowdimensional metal as discussed below.