SYNTHESIS AND CYCLIC VOLTAMMETRY OF TRINUCLEAR SULFIDO CLUSTERS OF NICKEL(II), PALLADIUM(II) AND PLATINUM(II) AND SELENIDO CLUSTERS OF NICKEL(II) WITH 1,2-BIS(DIPHENYL-PHOSPHINO)ETHANE, AND CRYSTAL-STRUCTURES OF SULFIDO AND SELENIDO CLUSTERS OF NICKEL(II)

The reaction between M2+ (M = Ni, Pd or Pt), 1,2-bis(diphenylphosphino)ethane (dppe), and NaSH or NaSeH in acetonitrile affords the trinuclear clusters [Ni3S2(dppe)3][BPh4]2.MeCN 1 [Ni3Se2(dppe)3][BPh4]2 2, [Pd3S2(dppe)3][PF6]2 3, and [Pt3S2(dppe)3][PF6]2.MeCN 4. The X-ray structures of [Ni3S2(dppe)3][PF6]2.MeCN and 2 were determined and cyclic voltammograms of 1-4 recorded. The structures of [Ni3S2(dppe)3]2+ and [Ni3Se2(dppe)3]2+ comprise three square-planar NiE2P2(E = S or Se) co-ordination planes sharing two mu-3-E ligands. The Ni-E, Ni ... Ni, and E ... E lengths for [Ni3S2(dppe)3]2+ are 2.192, 2.827 and 2.924(6) angstrom, while for 2 they are 2.311, 3.004 and 3.051 (4) angstrom, indicating a smaller central Ni3S2 core for [Ni3S2(dppe)3]2+ than the Ni3Se2 core of 2. Cyclic voltammograms of complexes 1 and 2 in dimethylformamide (dmf) at 293 K give two reduction peaks with associated oxidation peaks. Moreover, a broad oxidation peak appears at -0.87 V for 1. Two couples at -1.64 and -2.04 for 1 and at -1.59 and -1.87 V for 2 are reversible in acetonitrile solution at 255 K. The cyclic voltammogram of 3 in dmf gives only one reduction peak at a scan rate of 50 mV s-1 at 293 K, but at 255 K a reversible couple is exhibited at -1.96 V. A reduction peak at -2.10 V with an associated smaller oxidation peak at -2.07 V is observed for 4 in dmf at a scan rate of 50 mV s-1 at 293 K.