NICKEL THIOETHER CHEMISTRY - A REEXAMINATION OF THE ELECTROCHEMISTRY OF [NI([9]ANES3)2]2+ - THE SINGLE-CRYSTAL X-RAY STRUCTURE OF A NICKEL(III) THIOETHER COMPLEX, [NIIII([9]ANES3)2][H5O2]3[CLO4]6 ([9]ANES3 = 1,4,7-TRITHIACYCLONONANE)

Cyclic voltammetry of [Ni([9]aneS3)2][PF6]2 ([9]aneS3 = 1,4,7-trithiacyclononane) in MeCN (0.1 mol dm-3 NBu4PF6) at 293 K at platinum electrodes shows the previously reported chemically reversible oxidation at E1/2 = +0.98 V, DELTAE(p) = 82 mV and a quasi-reversible reduction at E1/2 = -1.11 V vs. ferrocene-ferrocenium, DELTAE(p) = 90 mV. These redox processes have been investigated spectroelectrochemically using ESR and electronic spectroscopy which indicate [Ni([9]aneS3)2]3+ to be a genuine d7 nickel(III) complex. The [Ni([9]aneS3)2]3+ cation can be generated quantitatively and stabilised for extended periods by dissolution of [Ni([9]aneS3)2]2+ in HClO4 solution. The complex [Ni(III)-([9]aneS3).][H5O2]3[ClO4]6 crystallises in the rhombohedral space group R3cBAR. The single-crystal X-ray structure confirms octahedral homoleptic thioether co-ordination with Ni-S bond lengths of 2.3129(25) angstrom. These Ni-S distances are significantly shorter than in the nickel(II) analogue [Ni([9]aneS3)2]2+ and confirm the formulation of a mononuclear nickel(III)-thioether complex cation. Cyclic voltammetry of [Zn([9]aneS3)2] [PF6]2 reveals one irreversible oxidation and one irreversible reduction at E(pa) = +1.30 and E(pc) = -1.77 V respectively at a scan rate of 400 mV s-1. Significantly, the redox potential for the oxidation of the zinc(II) species is more anodic than for the nickel(II) analogue.