Neutron spectroscopy within the S=5 ground multiplet and low-temperature heat capacity in an Fe-4 magnetic cluster - art. no. 104403

The transitions within the S=5 ground state of the tetrairon(III) molecular cluster Fe-4(OCH3)(6)(dpm)(6) (Hdpm = dipivaloylmethane) have been measure d by inelastic neutron scattering. The spectra have been interpreted by mea ns of an effective spin Hamiltonian for an isolated S=5 multiplet, taking i nto account the presence of three different isomers in the compound. It has been shown that for the two dominant isomers the symmetry of the zero-fiel d splitting tensor is not purely axial, but a nonzero rhombic coefficient E is needed to fit the neutron spectra. The results have been discussed in c omparison with recent high-field electron paramagnetic resonance data in si ngle crystals. Heat-capacity measurements in the range 2 to 20 K have been performed and shown to be compatible with the neutron results for the zero- field splitting.