Structural and magnetic studies of original tetranuclear CoII-LnIII complexes (LnIII = Gd, Tb, Y).
The syntheses, structural determinations and magnetic studies of tetranuclear Co(II)-Ln(III) complexes (Ln = Y, Gd, Tb) involving orthovanillin as main ligand are described. The structural studies demonstrate that centrosymmetric tetranuclear Co(2)-Ln(2) complex molecules with a defect-dicubane central core are obtained, with hexacoordinate Co ions in deformed octahedral environments and nine-coordinate lanthanide ions. The Co ions are linked by two hydroxo bridges and each Co ion is also involved in a double phenoxo-hydroxo bridge with the two Ln ions, so that each hydroxo group is triply linked to the two Co and one Gd ions. The four metal ions are coplanar. A ferromagnetic Co-Ln interaction operates in the Co(2)-Ln(2) complexes (Ln = Gd, Tb), along with a D zero-field splitting term for the cobalt ion and a weak ferromagnetic Co-Co interaction. The SMM behaviour of the Co(2)-Gd(2) complex is confirmed by observation of hysteresis loops, as a consequence of the slowing down of relaxation for this tetranuclear complex. The Co(2)-Tb(2) complex does not behave as a SMM, what could result from a subtractive combination of the Tb and Co anisotropies and an increased transverse anisotropy, leading to large tunnel splittings and quantum tunneling of magnetization.
CNRS, LCC, Laboratoire de Chimie de Coordination, 205, route de Narbonne, F-31077 Toulouse, France. costes@lcc-toulouse.fr
Jean-Pierre
JP
Costes
Laure
L
Vendier
Wolfgang
W
Wernsdorfer