MAGNETOSTRUCTURAL CORRELATIONS IN MAGNETICALLY COUPLED (MU-OXO)DIIRON(III) COMPLEXES

A quantitative magnetostructural relationship has been found for dinuclear iron(III) centers bridged by a ligand oxygen atom (oxo, hydroxo, alkoxo, etc.) and at least one other bridging ligand (carboxylate, sulfate, phosphate, etc.). A correlation exists between the antiferromagnetic exchange-coupling constant J (in cm-1) and P, a parameter having units of distance (in angstrom) defined as half the shortest superexchange pathway between two iron(III) ions. Specifically, -J = A exp(BP) where A = 8.763 x 10(11) and B = -12.663. Results for 36 dinuclear metal centers, including Fe2 and Fe3, complexes have been used to derive this relationship, which can also be applied to tetranuclear complexes and metalloproteins. This magnetostructural correlation is shown to have powerful predictive properties, although it does not apply to (mu-oxo)diiron(III) centers unsupported by other bridging ligands. Attempts to correlate J with any other structural parameters such as the Fe-O-Fe angle or Fe...Fe distance for ligand-bridged [Fe2O]4+ cores were unsuccessful.