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RESEARCH PRODUCT

Magnetism in Polyoxometalates: Anisotropic Exchange Interactions in the Co Moiety of [Co3W(D2O)2(ZnW9O34)2]12−—A Magnetic and Inelastic Neutron Scattering Study

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The ground-state properties of a Co moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2]⋅40 D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin–orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as ℋ=−2Σ(JŜ1αŜ2α+JŜ2αŜ3α), where Jα are the components of the exchange interactions between the CoII ions. To reproduce the INS data, different orientations of the two anisotropic J tensors must be considered, and the following conditions had to be introduced: J=J, J=J, J=J. This result was correlated with the molecular symmetry of the complex. The following set of parameters was obtained: J=J=1.37, J=J=0.218, and J=J=1.24 meV. This set also reproduces in a satisfactory manner the specific heat, susceptibility, and magnetization properties of Co3.