Magnetostructural correlations in polynuclear complexes:: The Fe4 butterflies

Theoretical methods based on density functional theory have been employed to analyze the exchange interactions in Fe-4 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.