title: An azophenine radical-bridged Fe2 single-molecule magnet with record magnetic exchange coupling.
abstract: One-electron reduction of the complex [(TPyA)2Fe(II)2((NPh)L(2-))](2+) (TPyA = tris(2-pyridylmethyl)amine, (NPh)LH2 = azophenine = N,N',N",N'''-tetraphenyl-2,5-diamino-1,4-diiminobenzoquinone) affords the complex [(TPyA)2Fe(II)2((NPh)L(3-•))](+). X-ray diffraction and Mössbauer spectroscopy confirm that the reduction occurs on (NPh)L(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 (NPh)L(3-•) in the reduced complex, giving an S = 7/2 ground state with an estimated coupling constant magnitude of |J| ≥ 900 cm(-1). Mössbauer 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.
authors.affiliation: Department of Chemistry, Northwestern University , Evanston Illinois 60208-3113, United States.
authors.forename: Ie-Rang
authors.initials: IeR
authors.lastname: Jeon
authors.forename: Jesse G
authors.initials: JG
authors.lastname: Park
authors.forename: Dianne J
authors.initials: DJ
authors.lastname: Xiao
authors.forename: T David
authors.initials: TD
authors.lastname: Harris