Dinuclear Fe(III) complexes with spin crossover

A series of dinuclear Fe(III) complexes was synthesized in which the Schiff-base blocking ligand L-5 coordinates each of the centers which are linked by a bidentate, bipyridine-type ligand. For these systems, [(LFeIII)-Fe-5{bridge} (FeL5)-L-III](BPh4)(2), thermally induced spin crossover is observed. The corollary of the systems is that the spin crossover interferes with the magnetic exchange interaction. The overlap of the energy bands of the LL and HH reference states (L, low-spin; H, high-spin) causes the exchange interaction to act against the spin crossover (leading to incompleteness or gradual behavior).