Low-energy spectrum of a Tm-based double-decker complex

The magnetic and electronic properties of a Tm-based "double- decker" phtalocyanine complex are extensively investigated by several spectroscopic (optical absorption, inelastic neutron-scattering) and bulk (specific-heat) techniques. The resulting low-energy spectrum is exploited to obtain direct information on the ligand field. We show that the literature value of the second-order parameter A20 is significantly overestimated and that the additional parameters arising from the true C4 point symmetry (instead of the usually assumed ideal D4d symmetry) at the rare-earth site cannot be neglected on this energy scale, while the presence of further symmetry reduction at low temperature is highly unlikely. The effect of the proposed ligand-field parameters on the relaxation properties of the Tb-based double-decker single-molecule magnet is briefly discussed.