CRYSTAL-STRUCTURES AND ELECTROCHEMICAL PROPERTIES OF 2 PHASES OF TETRABUTYLAMMONIUM BIS(1,3-DITHIOLE-2-THIONE-4,5-DISELENOLATO)-NICKELATE(III)

The crystal structures of two phases (alpha and beta) of [Bu4N]2[Ni(dSit)2]2 are reported (dsit = 1,3-dithiole-2-thione-4,5-selenolate). The compound crystallises either in blocks (alpha-phase) or needles (beta-phase). The alpha-phase crystallises in the triclinic space group P1BAR, with a = 12.381(3),b = 14.009(2), c = 9.571(1) angstrom, alpha = 94.43(1),beta = 99.61(2), gamma = 81.32(2)-degrees and Z = 1 with the asymmetric unit having the formula Ni2C44H72N2S12Se8. The beta-phase crystallises in the triclinic space group P1BAR, with a = 11.820(1), b = 14.998(1), c = 9.517(1) angstrom, alpha = 96.980(8), beta = 100.251(9), gamma = 76.926(8)-degrees and Z = 1 with the asymmetric unit having the formula Ni2C44H72N2S12Se8. The structures were solved by direct methods, and refined by Fourier and least-squares techniques. Both crystal structures differ only marginally. They consist of anionic dimers made up of two chemically bound Ni(dsit), units. The Ni atom is square pyramidally coordinated by five selenium donor atoms, with the apically bridging Ni-Se distances (2.48 and 2.47 angstrom for alpha-[Bu4N]2[Ni(dsit)2]2 and beta[Bu4N]2[Ni(dsit)2]2, respectively) being significantly longer than the equatorial distances (2.316-2.347 angstrom). In the beta-phase one of the thionyl groups and three of the four butyl chains of the cations are in disorder. Because of the bulky nature of the cations, no short interdimer contacts are present in the lattices. Cyclic voltammetry studies of [Bu4N]2[Ni(dsit)2]2 in acetone show a first reversible 2[Ni(dsit)2]- half arrow right over half arrow left[Ni(dSit)2]2(2-) couple at E1/2= -0.12 V (versus Ag/AgCl), and a second quasi-reversible couple involving a single anodic peak at 0.18 V and two reduction peaks at 0.08 and -0.01 V.