Antiferromagnetic Exchange in Triclinic Crystals of Tetra-$\mu $-Benzoato-bis(4-Methylquinoline) Dicobalt II

Abstract

The magnetic susceptibilities of tetra-$\mu $-benzoato-bis(4-methylquinoline) dicobaltII have been measured and interpreted within the theoretical model described in the preceding paper. Crystals of the title complex are triclinic, a circumstance which has lead to the development of a new technique for the measurement of triclinic crystal susceptibilities using a Faraday balance. The technique is discussed in general terms and is applicable with Faraday equipment employing either longitudinal or, as here, transverse magnetic fields. The magnetic tensor for this binuclear cobalt complex has been determined throughout the temperature range 20-300 K. Good agreement between these results and those calculated from the quantum mechanical model have been obtained in the temperature range 90-300 K. At lower temperatures, a probable small paramagnetic impurity prevents useful theoretical treatment. There emerges an unambiguous conclusion that the antiferromagnetic coupling between the cobalt atoms is almost completely determined by interaction between metal $xy$ orbitals, presumably via a superexchange process involving the delocalized$\pi $ bonding framework of the bridging carboxylate groups.