CRYSTAL-STRUCTURE AND ELECTRICAL AND MAGNETIC-PROPERTIES OF TRIS(N,N,N',N'-TETRAMETHYL-PARA-PHENYLENEDIAMINE) BIS(4,5-DIMERCAPTO-1,3-DITHIOLE-2-THIONATO)NICKELATE

The electrochemical synthesis and characterization of a new member of the family of [cat]x[Ni(dmit)2] coordination compounds, with "cat" being the radical cation of N,N,N',N'-tetramethyl-p-phenylenediamine (abbreviated as tmpd), dmit2- = C3S5(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate, and x = 3, is reported. [tmpd]3[Ni(dmit)2] has an extremely low electrical conductivity of about 10(-12) S cm-1. The high resistivity contrasts with many materials based on both [Ni(dmit)2] alone or tmpd alone. A single-crystal structure determination was carried out. The crystals are triclinic, space group P1BAR with a = 9.423 (1) angstrom, b = 9.883 (1) angstrom, c = 14.728 (2) angstrom, alpha = 102.99 (2)-degrees, beta = 93.33 (2)-degrees, gamma = 125.30 (2)-degrees, and Z = 1 for formula C36H48N6NiS10. The structure was solved by Patterson, Fourier, and least-squares techniques. R(w) = 0.043 for 3792 independent significant reflections. The Ni atoms are located at centers of symmetry. The unit cell contains three tmpd units, two of which being dimerized and one isolated. The structure displays shortests S...S contacts of about 4.2 angstrom; these very long contacts explain the observed high resistivity. The mean Ni-S distance is 2.193 angstrom, which indicates that the Ni atom carries an average positive charge of about 2.24. This picture is consistent with the EPR and susceptibility data, which can be explained by the occurrence of [Ni(dmit)2]- and [tmpd]2+ radicals, together with [Ni(dmit)2]2- anions and [tmpd]2(2+) dimers, the latter having a thermally accessible triplet state.