Valence electronic structure of sublimated Fe4 single-molecule magnets: an experimental and theoretical characterization

The valence electronic structures of two single-molecule magnets (SMMs), [Fe-4(L)(2)(dpm)(6)] and [Fe-4(L)(2)(pta)(6)], (Hdpm = dipivaloylmethane, Hpta = pivaloyltrifluoroacetone, L3- = Ph-C(CH2O)(3)(3-)), are investigated by means of ultraviolet photoemission spectroscopy (UPS) and ab initio calculations. The experimental UPS spectra of both compounds are analysed and compared with the total density of states (TDOS) computed with the hybrid functional PBE0. The substitution of half of the methyl groups in [Fe-4(L)(2)(dpm)(6)] with fluorine atoms in [Fe-4(L)(2)(pta)(6)] unexpectedly affects the spectrum shape in the Fermi region, thus becoming a useful fingerprint of the two SMMs. Moreover, a computational protocol at DFT + U level of theory is assessed on both compounds, which is in good agreement with the experimental spectroscopic and magnetic data. The basis for the future modelling of the adsorption of Fe-4 clusters on surfaces is established.