Sulphur-nitrogen chelating agents. VIII. Magnetic behaviour of some cobalt(II) complexes at the crossover region

Abstract

The bis-ligand cobalt(II) complexes of 6-methylpyrid-2-yi-N-(2?- methylthio-phenyl)methyleneimine (SNNMe) are spin-free and the corresponding complexes of 2-pyridyl-N-(2?- methylthiophenyl)methyleneimine (SNN) are spin-paired. This difference in magnetic behaviour arises from a lower effective ligand field strength of SNNMe, presumably due to the steric inter-ligand interference introduced by the methyl group in the 6-position of SNNMe. The moments of the cobalt(II) complexes are dependent on temperature and the departures from the Curie-Weiss law are quite anomalous. No quantitative treatment is given for the anomalous magnetic behaviour; however, the results are best explained as a thermal equilibrium between the nearly equi-energetic spin-paired and spin-free states of the cobalt(II) atom.