Kinetics and mechanism of electron-transfer reactions of bis(1,4,7-triazacyclononane)nickel-(II) and -(III) complexes
Abstract
The rates of the outer-sphere electron-transfer reactions involving the complex ion [NiL12]2+(L1= 1,4,7-triazacyclononane) with a series of substituted polypyridine iron(III) ions, [Fe(L–L)3]3+, and various macrocyclic nickel(III) species and of the reduction of [NiL12]3+ by [Co(L–L)3]2+ species have been measured. Use of a Marcus cross-correlation leads to a self-exchange rate for the [NiL12]3+/2+ couple of k22= 6 × 103 dm3 mol–1 s–1. The data are of interest in that, unlike most other NiII–NiIII couples measured, upon electron transfer there is retention of octahedral symmetry around the metal centre. Possible correlations of rates of electron exchange with bond extension in the primary co-ordination sphere are discussed.