Anomalous magnetic properties of planar bibridged trinuclear copper(II)-halide compounds

Abstract

The magnetic susceptibilities of five trinuclear pseudoplanar bibridged copper(II) chloride species have been measured from approximately 5 to 300 K. The compounds all show antiferromagnetic intratrimer and generally weaker ferromagnetic intertrimer spin coupling. These compounds show systematic deviations from the susceptibility as calculated from an isotropic Heisenberg Hamiltonian with nearest-neighbor coupling. The deviations arise from intertrimer interactions through the formation of semicoordinate bonds and result in a spin-frustrated state at low temperatures. The results of a phenomenological mean field theory model support spin-frustration occurrence by accurately modeling the non-Boltzmann depopulation of the excited quartet state. Preliminary cluster expansion calculations have not lent support to the postulate but more extended calculations may be necessary to include a sufficient number of intermolecular interactions in order to accurately describe the crystalline state.