Butterfly-like complexes

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 S_t = 0 and
S_t = 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 S_t = 1 to S_t = 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.