STRUCTURE AND PHYSICAL-PROPERTIES OF THE TETRAPHENYLPHOSPHONIUM-[NI(DMIT)(2)](3) (DMIT=2-THIOXO-1,3-DITHIOL-4,5-DITHIOLATE) SALT

Crystals of TPP-Ni[(dmit)(2)](3) (TPP = tetraphenylphosphonium, dmit = 2-thioxo-1,3-dithiol-4,5-dithiolate) were prepared. The structure of the crystal was determined as follows: monoclinic C2/c; a = 18.086(3) Angstrom, b = 7.184(2) Angstrom, c = 45.838(6) Angstrom, beta = 92.59(1)degrees, V = 5950(2) Angstrom(3), and Z = 4. In the crystal, the large counteractions separate the conducting sheet of Ni(dmit)(2) anions. Within the conducting sheet, two of the three Ni(dmit)(2) anions form columns, and remaining the Ni(dmit)(2) anion fills the spaces between the columns. The molecular plane of the Ni(dmit)(2) anions in the column is almost perpendicular to that of isolated Ni(dmit)(2). The electrical conductivity was nearly one-dimensional with the highest conductivity being observed parallel to the column direction. The inplane anisotropy of the conductivity was ca. 1:100. The crystal exhibited a conductivity of 10 S/cm at room temperature and semiconducting behavior at lower temperatures. Activation energies of 0.035 and 0.036 eV, respectively, were observed below and above 125 K. A deviation from Arrhenius behavior was observed above 160 K. The effect of pressure was relatively small. The crossover point between the two semiconducting regimes shifted to 80 K at 7 kbar and the activation energies decreased to 0.011 and 0.036 eV, respectively. The thermoelectric power was negative at room temperature in the column direction and showed an activation-type behavior with the crossover point around 125 K. Analysis of the reflectance spectra of the salt indicated that the gap was smaller than 0.09 eV, which is consistent with that of conductivity measurements and that the crystal is not exactly one-dimensional. The magnetic susceptibility obeyed the Curie-Weiss law below room temperature and one spin per three Ni(dmit)(2) units was calculated from the Curie constant. The distribution of electrons in the crystal is discussed.