A cyclic voltammetric study in acetonitrile and dichloromethane of the five-coordinate nickel complexes [Ni-(mtas)(2)](2+) (mtas = bis(2-(dimethylarsino)phenyl)methylarsine), [Ni(ptas)(2)](2+) (ptas = bis(2-(dimethylarsino)phenyl)phenylarsine), [Ni(L(2))(mtas)](2+) (L(2) = 1,2-bis(dimethylarsino)benzene (diars), 1,8-bis(dimethylarsino)naphthalene (dman), 1,2-bis(dimethylarsino)tetrafluorobenzene (F-4-diars)), and [Ni(L(2))(ptas)](2+) (L(2)= diars, dman) is reported. All nickel oxidation states from 0 to IV are formed within the accessible potential range and are stable with respect to disproportionation. Inspection of the electrochemical data identifies Ni-As bond formation and cleavage reactions accompanying electron transfer and reveals that Ni(I), Ni(II), and Ni(III) species are five-coordinate whereas Ni(0) and Ni(IV) species are four- and six-coordinate, respectively. The homoleptic Ni(IV) complexes have the As-6 donor set and are kinetically stable on the conventional cyclic voltammetric time scale. For the heteroleptic complexes, a molecule of solvent or an electrolyte anion coordinates to the Ni(IV) center and the kinetic stability is reduced. The thermodynamic and kinetic stabilities of the homoleptic complexes are compared to those of nickel complexes with (diars)(2) and (F-4-diars)(2) coordination. The electrode kinetics of the Ni(III/II) couple of all complexes studied exhibit a marked dependence on solvent, electrolyte, and electrode material. This is attributed, in part, to ion-pairing phenomena.