Molecular (super)conductors derived from bis-dithiolate metal complexes

The synthesis, electrochemical behavior, electrocrystallization and solution diffusion preparation of the M(dmit)(2) bis-dithiolate metal complexes (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolato) and derived non integral oxidation state compounds is briefly recalled. The properties of the eight superconductors known in this series, namely, [TTF][Ni(dmit)(2)](2), [Me4N](0.5)[Ni(dmit)(2)], alpha-[TTF][Pd(dmit)(2)](2), alpha'-[TFF][Pd(dmit)(2)](2), beta-[Me4N](0.5)[Pd(dmit)(2)], [Me2Et2N](0.5)[Pd(dmit)(2)], alpha-[EDT-TTF][Ni(dmit)(2)](2), and beta'-[Me2Et2P](0.5)[Pd(dmit)(2)], (TTF = tetrathiafulvalene, EDT-TTF = ethylenedithio-tetrathiafulvalene) are described, including crystal structures, conductivities, IR/Raman studies, temperature/pressure phase diagrams, observation of charge density waves, and band structure calculations. The enlargement of this series of conducting compounds, not only by modification of the inorganic countercation or the organic cation radical, but also by modification of the dmit ligand itself, is reviewed, but superconductivity seems to be restricted to the dmit-based systems. The studies on these conducting bis-dithiolate metal compounds have been extended to other properties and utilization, such as, for example, conducting Langmuir-Blodgett films, unconventional magnetic properties, and nonlinear optics (NLO). Recent tentative research works on the interplay of conducting, magnetic and NLO properties in such compounds are reported. (C) 1999 Elsevier Science S.A. All rights reserved.