NEW SYNTHETIC METALS BASED ON [M(DMIT)2] COMPLEXES, M = NI, PD, PT

i) Systematic study of the series [NHyMe4-y]x[M(dmit)2], M = Ni, Pd, P t, DC resistivity measurements performed on [NHMe3][Ni(dmit)2]2 show s trong non-linearity effects at low temperature. Three new conducting p hases with stoichiometries x = 0.5 (M = Ni ; y = 2) and x = 0.4 ( M = Ni ; y = 1, 3) display a semi-conductive behavior (sigma(RT) = 0.08, 0 .2 and 1.5 S/cm respectively) ; they are built of stacks of weakly dim erized [Ni(dmit)2] units. The conductivity of [NHMe3][Pt(dmit)2]3,CH3C N (sigma(RT) approximately 140 S/cm) is the highest observed for a [Pt (dmit)2]-based system ; it remains constant down to ca. 180 K and then drops sharply ; the crystal structure consists of stacks of [Pt(dmit) 2]2 dimers. ii) The D-A complex (EDT-TTF)2[Pd(dmit)2]2 is metallic dow n to 0.5 K (sigma(RT) = 55 S/cm). A resistivity bump, observed at 35 K at ambient pressure, is shifted towards lower temperature by applying pressure and disappears above 5 kbar. This could be interpretated in terms of condensation of a charge density wave.