title: Magnetic and optical studies on an S = 6 ground-state cluster [Cr12O9(OH)3(O2CCMe3)15]: determination of, and the relationship between, single-ion and cluster spin Hamiltonian parameters.
abstract: The dodecametallic Cr(III) cluster [Cr(12)O(9)(OH)(3)(O(2)CCMe(3))(15)] has a ground spin state of S = 6 characterized by the spin Hamiltonian parameters g(ZZ)() = 1.965, g(XX)() = g(YY)() = 1.960, D(S=)()(6) = +0.088 cm(-)(1), and E(S=)()(6) = 0 (where D and E are the axial and rhombic zero-field splitting parameters, respectively) as determined by multifrequency EPR spectroscopy and magnetization studies. Micro-SQUID magnetization studies reveal steps due to the fine structure of the ground state, with the spacing between the steps in excellent agreement with the D(S=)()(6) value determined by EPR. Analysis of high-resolution optical data (MCD) allows us to determine the single-ion g values and D value (= -1.035 cm(-)(1)) of the constituent Cr(III) ions directly. A vector coupling analysis demonstrates that the cluster ZFS is almost entirely due to the single-ion component. Thus, the relative orientations of the local and cluster magnetic axes can lead to a cluster ZFS of opposite sign to the single-ion value, even when this is the only significant contribution.
authors.affiliation: Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Mark
authors.initials: M
authors.lastname: Murrie
authors.forename: Vasily S
authors.initials: VS
authors.lastname: Oganesyan
authors.forename: Stergios
authors.initials: S
authors.lastname: Piligkos
authors.forename: Nigel R J
authors.initials: NR
authors.lastname: Poolton
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
authors.forename: Graham M
authors.initials: GM
authors.lastname: Smith
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Thomson
authors.forename: Grigore A
authors.initials: GA
authors.lastname: Timko
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wernsdorfer
authors.forename: Richard E P
authors.initials: RE
authors.lastname: Winpenny
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McInnes