Nuclear magnetic resonance studies of low-spin complexes of cobalt(II) with Schiff bases. NN′-1,1-dimethylethylenebis(salicylideneiminato)cobalt(II) in pyridine

Abstract

Isotropic paramagnetic proton n.m.r. shifts have been measured for the low-spin title complex in [²H₅]pyridine. The temperature dependence of the shifts shows large deviations from the Curie law. The deviation is interpreted in term of the effects of temperature-dependent ligand field on mixing of excited electronic configurations with the ground state. The contact shifts evaluated from the isotropic shifts are shown to arise from spin delocalization through both σ and π orbitals. the latter having a smaller contribution than the former. The pattern of the contact shift is explained by the ground-state configuration of Co^II where the unpaired electron is primarily in the d_z² orbital, and by the non-planar structure of the complex.