title: Magnetic polyoxometalates: anisotropic exchange interactions in the moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-.
abstract: The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) 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 Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties of the isosceles triangular Co(3) spin cluster is anisotropic and is expressed as H = - 2sigma(alpha)(=)(x,y,z)(J(alpha)(12)S(1alpha)S(2alpha) + J(alpha)(23)S(2alpha)S(3alpha) + J(alpha)(13)S(1alpha)S(3alpha)), where J(alpha) are the components of the exchange interactions between the Co(II) 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: J(x)(12) = J(y)(13) = 8.6 cm(-1); J(y)(12) = J(x)(13) = 1.4 cm(-1); J(z)(12) = J(z)(13) = 10.0 cm(-1); J(x)(23) = J(y)(23) = 6.5 cm(-1) and = 3.4 cm(-1).
authors.affiliation: Instituto de Ciencia Molecular, Universitat de València, c/ Dr. Moliner, Burjassot, Spain. juan.m.clemente@uv.es
authors.forename: Juan Modesto
authors.initials: JM
authors.lastname: Clemente-Juan
authors.forename: Eugenio
authors.initials: E
authors.lastname: Coronado
authors.forename: Alejandro
authors.initials: A
authors.lastname: Gaita-Ariño
authors.forename: Carlos
authors.initials: C
authors.lastname: Giménez-Saiz
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Güdel
authors.forename: Andreas
authors.initials: A
authors.lastname: Sieber
authors.forename: Roland
authors.initials: R
authors.lastname: Bircher
authors.forename: Hannu
authors.initials: H
authors.lastname: Mutka