Realization of the one-dimensional anisotropic XY model in a Tb(III)-W(V) chain compound.

We report the magnetic behavior of the one-dimensional (1D) cyanido-bridged chain complex [Tb(pzam)(3)(H2O)M(CN)(8)]center dot H2O, where M = W(V). The system shows qualitatively similar magnetic behavior with its already reported M = Mo(V): a broad anomaly in the specific heat ascribed to the magnetic interactions, a transition to three-dimensional magnetic order at T-C = 1.15 K, and comparable magnetization and susceptibility. However, substituting the Mo(V) ion by the larger W(V) causes a drastic change in the symmetry of the Tb(III) g tensor, whereby the magnetic interaction between the Tb(III) and M(V) changes from Ising type into an anisotropic XY exchange. We analyze the data in terms of theoretical predictions for the 1D XYZ Hamiltonian and we find an excellent agreement between the theory and experimental data (J(x) = 1.89 K, J(y) = 2J(x), J(z) = 0).