Structural and magnetic investigations on new molecular quantum rings

We report on a comparative investigation of the structural and magnetic properties of three oxygen-bridged polynuclear (N = 6, 8, 10) Cu(II) cyclomethylsiloxanolate complexes, Cu6[(MeSiO2)6]2·6DMF (1), {Cu8[(MeSiO2)8]2·8DMF}·EtOH (2) and {Cu10[(MeSiO2)10]2·10DMF}·6DMF (3). All three molecular complexes have a planar ring-shaped configuration of the copper S = 1/2 spins. The analysis of the magnetic data, with particular emphasis placed on the high-temperature behaviour, together with the structural information enables us to correlate the evolution of the exchange coupling J between the magnetic S = 1/2 centers of the quantum ring as a function of the number N of magnetic sites to the structural changes of the molecular crystals.