Influence of ligand flexibility on the electronic structure of oxidized Ni^III-phenoxide complexes

One-electron-oxidized Ni^III-phenoxide complexes with salen-type ligands, [Ni(salen)py₂]²⁺ ([1^en-py]²⁺) and [Ni(1,2-salcn)py₂]²⁺ ([1^cn-py]²⁺), with a five-membered chelate dinitrogen backbone and [Ni(salpn)py₂]²⁺ ([2^pn-py]²⁺), with a six-membered chelate backbone, have been characterized with a combination of experimental and theoretical methods. The five-membered chelate complexes [1^en-py]²⁺ and [1^cn-py]²⁺ were assigned as Ni^III-phenoxyl radical species, while the six-membered chelate complex [2^pn-py]²⁺ was concluded to be a Ni^II-bis(phenoxyl radical) species with metal-centered reduction in the course of the one-electron oxidation of the Ni^III-phenoxide complex [2^pn-py]⁺. Thus, the oxidation state of the one-electron-oxidized Ni^III salen-type complexes depends on the chelate ring size of the dinitrogen backbone.