Collison David, Murrie Mark, Oganesyan Vasily S, Piligkos Stergios, Poolton Nigel R J, Rajaraman Gopalan, Smith Graham M, Thomson Andrew J, Timko Grigore A, Wernsdorfer Wolfgang, Winpenny Richard E P, McInnes Eric J L
Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
Inorg Chem. 2003 Aug 25;42(17):5293-303. doi: 10.1021/ic034541b.
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.
