This paper presents a detailed study of solid-state structure, oxidation state, and electron transport in Ni(dpg)//2I and Pd(dpg)//2I, dpg equals diphenylglyoximato. The crystal structure of Ni(dpg)//2I has been studied by X-ray diffraction at 23 and minus 160 degree C. The crystal structure consists of stacked Ni(dpg)//2 units (staggered by 90 degree ) and disordered chains of iodine atoms extending in the c direction. At minus 160 degree C the Ni-Ni separation is 3. 223 (2) A; other important distances are Ni-N equals 1. 868 (15), N-C equals 1. 33 (3), N-O equals 1. 34 (3) A. Iodination brings about an increase in conductivity of greater than 10**8 (Ni) and greater than 10**7 (Pd), which is especially noteworthy since the only major change in crystal structure upon iodination is a ca. 0. 27 A decrease in the M(dpg)//2 stacking distance. Variable-temperature studies show the Ni(dpg)//2I and Pd(dpg)//2I conductivities to be thermally activated, with activation energies of 0. 19 plus or minus 0. 01 and 0. 54 plus or minus 0. 11 eV, respectively. Extensive experimental data are presented which demonstrate conclusively that M(dpg)//2I compounds, M equals Ni, Pd, contain the M(dpg)//2 units in formal fractional oxidation states, ca. plus 0. 2. It is shown that the diffuse X-ray scattering, resonance Raman, and iodine-129 Moessbauer techniques are powerful complementary methods for polyiodide structure identification, and hence for direct measurement of charge distribution in mixed-valence structures.
|Number of pages||16|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - Jan 1 1979|
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