Magnetic anisotropy of two cyclic hexanuclear Fe(III) clusters entrapping alkaline ions

The magnetic anisotropy of the two cyclic hexanuclear Fe(III) clusters [Li subset of Fe6L6]Cl . 6CHCl(3) and [Na subset of Fe6L6]Cl . 6CHCl(3), L = N( CH2CH2O)(3), was investigated. Based on a spin Hamiltonian formalism, the m agnetic anisotropy was calculated exactly to first order, i.e., in the stro ng exchange limit, using Bloch's perturbational approach and irreducible te nsor operator techniques. Experimentally, the magnetic anisotropy was inves tigated by magnetic susceptibility and high-field torque magnetometry of si ngle crystals as well as inelastic neutron scattering. It is demonstrated t hat torque magnetometry provides a valuable tool for the study of magnetic anisotropy in spin cluster complexes. The experimental data could be accura tely reproduced by;he calculations, and the different methods yield consist ent values for the coupling constants and zero-field-splitting parameters. Both the anisotropy and the exchange interaction parameter are found to inc rease with increasing Fe-O-Fe angle.