An Azophenine Radical-Bridged Fe2 Single-Molecule Magnet with Record Magnetic Exchange Coupling

One-electron reduction of the complex [(TPyA)(2)Fe-2(II)(L-NPh(2-))](2+) (TPyA = tris(2-pyridylmethyl)-amine, (LH2)-L-NPh = azophenine = N,N',N '',N'-tetraphenyl-2,5-diamino-1,4-diiminobenzoquinone) affords the complex [(TPyA)(2)Fe-2(II)(L-NPh(3-center dot))](+). X-ray diffraction and Mossbauer spectroscopy confirm that the reduction occurs on L-NPh(2-) to give an S = 1/2 radical bridging ligand. Dc magnetic susceptibility measurements demonstrate the presence of extremely strong direct antiferromagnetic exchange between S = 2 Fe-II centers and L-NPh(3-center dot) in the reduced complex, giving an S = 7/2 ground state with an estimated coupling constant magnitude of vertical bar J vertical bar >= 900 cm(-1). Mossbauer spectroscopy and ac magnetic susceptibility reveal that, this complex behaves as a single-molecule magnet with a spin relaxation barrier of U-eff = 50(1) cm(-1). To our knowledge, this complex exhibits by far the strongest magnetic exchange coupling ever to be observed in a single-molecule magnet.