Metal-like behavior, 1,2-dithiolenes

In spite of the large number of dithiolene complexes synthesized, 50 of their derived compounds exhibit a metal-like behavior at a temperature close to RT and within a significant temperature range. These compounds, listed in Tables I-IV, together with the relevant references and some details about their electrical behavior are either NIOS salts or D-A adducts. For the NIOS salts of dmit and mnt complexes, the associated counterions are mostly closed-shell cations such as alkyl-ammonium or sulfonium, or alkaline metal cations. For the D-A adducts derived from dmit and mnt acceptor complexes, the associated donors are TTF-like molecules and Per, respectively. The dddt complexes deserve special mention as the derived metal-like conductors involve M(dddt)2 v - cation radicals (instead of anion-radicals as in dmit or mnt systems). 

Very few dithiolene platinum complex-based compounds have been reported and most of them exhibit poor electrical conductivity (9, 122, 123). The complex (Me4N)[Pt(dmit)2]2 does show metal-like behavior (RT conductivity = 10 S cm 1) but only >220 K (123). Another exception is (NHMe3)[Pt(dmit)2]3. This compound, which has the unusual 1 3 stoichiometry, behaves as a metal down to 180 K, with a room temperature conductivity of 140 S cm-1 (91). The Pt(dmit)2 units form pairs with an eclipsed overlap mode. Unlike the analogue Ni derivatives (see above) substituting one hydrogen atom for one methyl group in the (Me4N)+ cation leads to an improvement in the electrical properties. 

Other Dithiolene Compounds Exhibiting Metal-Like Behavior... 

As with most molecule-based solids, most of the dithiolene complex-based solids are insulators, or, at best, semiconductors, which can hardly be considered as a remarkable property. Therefore, in the following sections we focus on systems exhibiting metal-like or superconducting behavior. 

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