Electron transfer between nickel(IV) oxime-imine complexes and nitrite: kinetics and mechanism

The oxidation of nitrite ion by two nickel(IV) oxime-imine complexes, [Ni-IV(L-1)](2+) and [Ni-IV(L-2)(2)](2+) (where H2L1 = 3,14-dimethyl-4,7,10,13-tetraazahexadeca dioxime and HL2 = 6-amino-3-methyl-4-azahex-3-en-2-one oxime) has been investigated in aqueous perchlorate medium in the range pH 4.50-7.00 by UV-vis spectrophotometry. The reduction of [Ni-IV(L-2)(2)](2+) involves 2 e(-) transfer (one-step) path at pH less than or equal to 6.0 and above this, it shows biphasic steps involving Ni-III as intermediate. The reduction of [Ni-IV(L-1)](2+) is, however, biphasic in nature throughout the.whole range of pH studied. The reaction rate exhibits a notable dependence on the product Ni-II complex added externally. The experimental findings and the low value of the calculated ion-pair constant suggest that the mode of electron transfer is likely to be of outer-sphere type. (C) 1998 Elsevier Science Ltd. All rights reserved.