A new molecular metal based on Pd(dmit)2:: synthesis, structure and electrical properties of (C7H13NH)[Pd(dmit)2]2 (dmit2-=2-thioxo-1,3-dithiole-4,5-dithiolate)

Air-oxidation of the acetone-acetic acid solution Of (C7H13NH)(2)[Pd(dmit)(2)] yielded black shiny platelets of (C7H13NH)[Pd(dmit)(2)](2). The crystal structure was characterized by a criss-cross columnar structure, which has been often observed in M(dmit)(2)-based (M = Ni, Pd) superconductors. Although the quinuclidinium cation (C7H13NH)(+) is found to be orientationally disordered on a 2-fold axis, the crystal exhibited metallic conductivity down to similar to 40 K. Under ambient pressure the room temperature conductivity is around 22 S cm(-1) and the resistivity gradually decreased with decreasing temperature down to 200 K, where it suddenly started to decrease more rapidly and kept decreasing down to similar to 40 K, where it started to increase steeply. At ea. 200 K the structural transition occurred, yet the crystal and molecular structures remained practically unaffected including the cation site disorder and the strong dimerization of the Pd(dmit)(2) molecules. The electrical behaviour under high pressure was rather unusual but could be compared with structurally related Pd(dmit)(2)-based superconductors.