The Electronic Structure of (Diiminopyridine)cobalt(I) Complexes

DFT calculations show that square‐planar LCoIR complexes of a diiminopyridine ligand are best regarded as containing low‐spin CoII antiferromagnetically coupled to a ligand radical anion. The lowest triplet state, corresponding to a 3d z 2⇄π* excitation, is calculated to be only a few kcal/mol above the ground state, and is thermally accessible. The anomalous 1H NMR chemical shifts of the LCoR complexes are suggested to be due to thermal population of the triplet state at room temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)