Magnetic Polyoxometalates: Anisotropic Exchange Interactionss in the CoII3 Moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-

The magnetic exchange interactions in a Co3II moiety encapsulated in Na17 [(NaOH2)Co3(H2O)(P2W15O56)2] (NaCo3) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co3O14 triangular cluster core consists of three octahedrally oxo-coordinated CoII ions sharing edges. According to the single-ion anisotropy and spin−orbit coupling usually assumed for octahedral CoII ions, the appropiate exchange Hamiltonian to describe the ground-state properties of the isosceles triangular Co3 spin cluster is anisotropic and is expressed as Ĥ = − 2∑α=x,y,z( Ŝ1αŜ2α + Ŝ2αŜ3α + Ŝ1αŜ3α), where Jα are the components of the exchange interactions between the CoII ions. To reproduce the INS data, nonparallel anisotropic exchange tensors needed to be introduced, which were directly connected to the molecular symmetry of the complex. The following range of parameters (value ± 0.5 cm-1) was found to reproduce all experimental information while taking magnetostructural relations into account: = = 8.6 cm-1; = = 1.4 cm-1; = = 10.0 cm-1; = = 6.5 cm-1 and = 3.4 cm-1.