Abstract

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 ∼ 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 ∼ 40 K, where it started to increase steeply. At ca. 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.