In collaboration with Prof. P. Chaudhuri (Mülheim) we have investigated ground spin state variations in carboxylate-bridged tetranuclear [Fe2Mn2O2]8+ cores and a comparison with their [Fe4O2]8+ and [Mn4O2]8+ congeners. Complexes with the Fe4O2 core and the Mn4O2 core possess an St = 0 and
St = 3 ground state, respectively, regardless of the nature of the bridging carboxylate ligand. In contrast, changing the bridging carboxylates in the [Fe2Mn2O2] core from acetate to diphenylglycolate, triphenyl acetate, benzoate, chloroacetate and propionate, results in a variation of the ground state from St = 1 to St = 3 due to spin frustration of the "body" manganese centres. The spin-correlation diagram for the Fe2Mn2O2 butterfly arrangement clearly demonstrates the ground state variation as a function of the ratio of two competing coupling interactions.
Energy-level diagram for a [Fe2Mn2O2]8+-butterfly complex. Dependence of the ground state from the ratio of both present coupling constants.