Some mesoscopic rings: Exact simulations and experiment

A numerical transfer-matrix approach and an exact diagonalization technique exploiting the point-group symmetry are worked out in the framework of qua ntum statistical mechanics and group theory for finite rings. They are appl ied to spin models of the high nuclearity cyclic dusters [Mn(hfac)(2)NITPh] (6) and Ni-12(O2CMe)(12)(chp)(12)(H2O)(6)(TRF)(6). The microscopic paramete rs of both molecules (J/k(B) = 350+/-10 K and J/k(B) = 8.5 K+/-0.5, g = 2.2 3+/-0.01, respectively) are then obtained from a fit of the theoretical sus ceptibility curves to the experimental results which are supplemented for N i-12 by new low-temperature measurements.