Quantum chemical calculations for the geometry and intramolecular rearrangements of a model nickel(<Emphasis Type="SmallCaps">ii</Emphasis>) <Emphasis Type="Italic">o</Emphasis>-semiquinone complex with a PCP pincer ligand

The structure and intramolecular rearrangements of the model five-coordinate nickel PCP-pincer complex with the o-semiquinone ligand were studied by the density functional theory method at the B3LYP/6-311++G(d,p) level. The isomerization associated with swing vibrations of the o-semiquinone ligand can occur virtually barrierless (0.7 kcal mol⁻¹). The dynamics of the coordination sphere determined by pendulum vibrations of the o-semiquinone ligand has the energy barriers of 4–5 kcal mol⁻¹, which is in good agreement with experimental data. A comparison of the results of calculations with the ESR spectroscopic data revealed the dependence of the types and the energy characteristics of intramolecular rearrangements on the nature of substituents at the phosphorus atom.