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⁺ (<b>[1</b>^<b>en</b><b>-py]</b>^<b>2+</b>) and [Ni­(1,2-salcn)­py₂]²⁺ (<b>[1</b>^<b>cn</b><b>-py]</b>^<b>2+</b>), with a five-membered chelate dinitrogen backbone and [Ni­(salpn)­py₂]²⁺ (<b>[2</b>^<b>pn</b><b>-py]</b>^<b>2+</b>), with a six-membered chelate backbone, have been characterized with a combination of experimental and theoretical methods. The five-membered chelate complexes <b>[1</b>^<b>en</b><b>-py]</b>^<b>2+</b> and <b>[1</b>^<b>cn</b><b>-py]</b>^<b>2+</b> were assigned as Ni^III-phenoxyl radical species, while the six-membered chelate complex <b>[2</b>^<b>pn</b><b>-py]</b>^<b>2+</b> 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 <b>[2</b>^<b>pn</b><b>-py]</b>^<b>+</b>. Thus, the oxidation state of the one-electron-oxidized Ni^III salen-type complexes depends on the chelate ring size of the dinitrogen backbone