Comparison of the Spin Dynamics in Different Types of Molecular Magnetic Rings from H-1 NMR

Proton spin-lattice relaxation (NSLR) measurements were performed in two mol. Cu magnetic rings contg. 6 and 8 spins (S = 1/2), resp., in an almost coplanar arrangement to probe the spin dynamics of the spins in the ring. The NSLR results obtained in the Cu6 and Cu8 rings as a function of temp. and of applied magnetic field are compared with previous results of NSLR of 1H in the Fe(III) rings Fe6 and Fe10 (S = 5/2). At room temp., common features are found in the spin dynamics while at low temp., when correlation effects become important, important differences are obsd. in the rings depending on the kind of coupling between magnetic spins (ferromagnetic or antiferromagnetic) and on the spin value S.