The magnetic anisotropy of the cyclic octanuclear Fe(III) cluster [Cs subsetFe(8)[N(CH(2)CH(2)O)(3)](8)]Cl was investigated. Based on a spin Hamiltonian formalism and the consequent use of all symmetries, the magnetic anisotropy could be calculated exactly to first order, i.e., in the strong exchange limit. Experimentally, the magnetic anisotropy was investigated by magnetic susceptibility and high-field torque magnetometry of single crystals. The field and angle dependence of the torque at 1.7 K could be accurately reproduced by the calculations with one single parameter set, providing accurate results for the coupling constant and single-ion zero-field-splitting. These magnetic parameters are compared to those of several related hexanuclear ferric wheels and are discussed with respect to magneto-structural correlations for both coupling constant and single-ion anisotropy.

The magnetic anisotropy of the two cyclic hexanuclear Fe(III) clusters [Li⊂Fe 6 L 6 ]Cl‚6CHCl 3 and [Na⊂Fe 6 L 6 ]-Cl‚6CHCl 3 , L ) N(CH 2 CH 2 O) 3 , was investigated. Based on a spin Hamiltonian formalism, the magnetic anisotropy was calculated exactly to first order, i.e., in the strong exchange limit, using Bloch's perturbational approach and irreducible tensor operator techniques. Experimentally, the magnetic anisotropy was investigated by magnetic susceptibility and high-field torque magnetometry of single crystals as well as inelastic neutron scattering. It is demonstrated that torque magnetometry provides a valuable tool for the study of magnetic anisotropy in spin cluster complexes. The experimental data could be accurately reproduced by the calculations, and the different methods yield consistent values for the coupling constants and zero-field-splitting parameters. Both the anisotropy and the exchange interaction parameter are found to increase with increasing Fe-O-Fe angle.