Synthesis, electrical behaviour, and crystal and electronic band structures of two different phases of the (SMeEt2)[Pd(dmit)(2)](2) salt. Consequences of cationic disorder on the electrical properties

The previously mentioned (SMeEt2)[Pd(dmit)(2)](2) (1) and the new (SMeEt2)( 0.5)[Pd(dmit)(2)] (2) phases are obtained by electrocrystallisation of (SMe Et2)(2)[Pd(dmit)(2)] in acetonitrile. The crystal structures of 1 and 2 are determined by X-ray diffraction methods, both at room and low temperatures . Though not previously detected, a cation disorder is evidenced in both ph ases at room temperature which is removed in 1 at low temperatures. Conduct ivity measurements show a rather smooth metal to insulator transition in th e 150-200 K range for 1 whereas 2 behaves as a semiconductor in the whole r ange of temperature. Under pressure, the transition of 1 is shifted down to lower temperatures and becomes more abrupt. Electronic band structure calc ulations (by means of the extended Huckel tight-binding model) show that th e cation disorder evidenced in 1 is responsible for two different electron transfers occurring from the (SMeEt2)(+) cation layers to the two crystallo graphically independent anion layers, resulting thus in the observed room t emperature metal-like behaviour of 1. The ambient pressure phase transition of 1 is shown to be the consequence of a more homogeneous electron transfe r, possibly leading to a Mott-Hubbard localised state at low temperatures, as is also the case for 2. Under pressure, the more abrupt phase transition observed in 1 is believed to originate from a different metallic regime.