Paramagnetic anisotropy and electronic structure of [NN′-ethylenebis-(salicylideneiminato)]cobalt(II), its pyridine adduct, and [NN′-ethylene-bis(thiosalicylideneiminato)]cobalt(II)

Abstract

Single-crystal magnetic-anisotropy measurements have been made over the temperature range 80–300 K on the oxygen-inactive title chelates [{Co(salen)}₂], [Co(salen)]′py· and [{Co(tsalen)}₂]. These five-co-ordinate species all show rhombic magnetic ellipsoids wth [{Co(tsalen)}₂] being the least anisotropic. Both salen corn-plexes display an unusually rapid increase in magnetic moment at higher temperatures. The theoretical model developed to interpret the results incorporates spin–orbit coupling between the ground doublet state and the excited doublet and quartet states, the latter being low-lying and important in the case of the salen complexes. Small changes in ligand field with temperature have been invoked to explain the rapid increases in µ_i at higher temperatures. The relative ordering of the cobalt d-orbital levels has been deduced, and correlations between the positions of the out-of-plane π orbitals, d_xz and d_yz, and the bonding of the axial donor ligands (e.g. pyridine) and O₂, are briefly discussed.