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.

The structure of vaterite-type rare earth orthoborate (LnBO3) has long been a subject of interest and controversy. In the present work, the crystal structures of two polymorphs of the vaterite-type rare earth orthoborates, i.e., the low- and high-temperature modifications of (Y0.92Er0.08)BO3, were solved and refined from neutron powder diffraction data. The low-temperature polymorph crystallizes in a C-centered monoclinic cell with C2/c space symmetry, the unit cell parameters being a = 11.3138(3) Å, b = 6.5403(2) Å, c = 9.5499(2) Å, and β = 112.902(1)°. The boron atoms in the structure are all tetrahedrally coordinated and form the three-membered ring borate B3O9 groups. The high-temperature form crystallizes in a new structure type in a monoclinic cell with C2/c space symmetry, and the unit cell constants a = 12.2019(3) Å, b = 7.0671(2) Å, c = 9.3424(2) Å, and β = 115.347(1)°. The borate groups in the high-temperature structure are all isolated flat BO3 triangles. As far as the structural chemistry is concerned, both structures are different from the typical CaCO3 vaterite. However, they do share some common features, particularly the packing fashion of the cations, which results in similarly looking X-ray diffraction patterns as that of the typical vaterite.

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