Finite-temperature characterization and simulations of the molecular assemblies Mn-6 and Ni-12

Numerical transfer-matrix approach and exact diagonalization technique expl oiting the point-group symmetry and the properties of the shift operator ar e worked out in the framework of quantum statistical mechanics for the isot ropic Heisenberg spin Hamiltonian with the ring geometry. They are applied in large-scale simulations to the title high nuclearity cyclic clusters Mn- 6 (i.e. [Mn(hfac)(2)NITPh](6)) and Ni-12 (i.e. Ni-12(O2CMe)(12)(chp)(12)(H2 O)(6)(THF)(6)) in order to model quantitatively their magnetic properties. For Ni-12 complex new experimental susceptibility data are also reported. N ew microscopic spin model parameters for both molecules are obtained from a fit of the theoretical susceptibility curves to the experimental results.