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Magnetostructural correlations in polynuclear complexes: the Fe4 butterflies.

Theoretical methods based on density functional theory have been employed to analyze the exchange interactions in Fe4 butterfly complexes. Three exchange coupling constants, calculated using a hybrid functional, provide an accurate description of the experimental magnetic susceptibility. The largest coupling constant corresponds to the interaction between the central and external iron atoms and presents a strong dependence on the Fe-O bond distance and the Fe-O-Fe angle of the central Fe2O2 core. An excellent linear correlation is found between such exchange coupling constants and a function of the spin population of the iron atoms, that is related with the square of the overlap of the "magnetic orbitals", according to the Kahn-Briat model.