Probing Magnetic Excitations in CoII Single-Molecule Magnets by Inelastic Neutron Scattering

Co(acac)(2)(H2O)(2) (1, acac = acetylacetonate), a transition metal complex (S = 3/2), displays field-induced slow magnetic relaxation as a single-molecule magnet. For 1 and its isotopologues Co(acac)(2)(D2O)(2) (1-d(4)) and Co(acac-d(7))(2)(D2O)(2) (1-d(18)) in approximately D-4h symmetry, zero-field splitting of the ground electronic state leads to two Kramers doublets (KDs): lower energy M-S = +/- 1/2 (phi(1,2)) and higher energy M-S = +/- 3/2 (phi(3,4)) states. This work employs inelastic neutron scattering (INS), a unique method to probe magnetic transitions, to probe different magnetic excitations in 1-d(4) and 1-d(18). Direct-geometry, time-of-flight Disk-Chopper Spectrometer (DCS), with applied magnetic fields up to 10 T, has been used to study the intra-KD transition as a result of Zeeman splitting, M-S = -1/2 (phi(1)) -> M-S = +1/2 (phi(2)), in 1-d(18). This is a rare study of the M-S = -1/2 -> M-S = +1/2 excitation in transition metal complexes by INS. Indirect-geometry INS spectrometer VISION has been used to probe the inter-KD, ZFS transition, M-S = +/- 1/2 (phi(1,2)) -> M-S = +/- 3/2 (phi(3,4)) in both 1-d(4) and 1-d(18), by variable-temperature (VT) properties of this excitation. The INS spectra measured on VISION also give phonon features of the complexes that are well described by periodic DFT phonon calculations.