ANISOTROPIC EXCHANGE COUPLING IN THE KEGGIN DERIVATIVE K-8[CO-2(D2O)(W11O39)]CENTER-DOT-ND(2)O

20 g of the fully deuterated title compound have been prepared in poly crystalline form and investigated by inelastic neutron scattering usin g both thermal and cold neutrons, Magnetic dimer excitations were obse rved and the energy-splitting pattern resulting from the exchange coup ling within the Co2+ dimer was determined. The coupling is highly anis otropic with the parameter values J = -2.24 meV and eta = 0.33 based o n the effective coupling Hamiltonian (H) over cap = - 2J[S1zS2z + eta( S1xS2x + S1yS2y)]. The anisotropy results mainly from the single-ion a nisotropy of the Co2+ ion in the distorted octahedral coordination. (C ) 1998 Elsevier Science B.V. All rights reserved.