title: Structural and spectroscopic studies of valence-delocalized diiron(II,III) complexes dupported by carboxylate-only bridging ligands.
abstract: The synthesis, molecular structures, and spectroscopic properties of a series of valence-delocalized diiron(II,III) complexes are described. One-electron oxidation of diiron(II) tetracarboxylate complexes afforded the compounds [Fe(2)(mu-O(2)CAr(Tol))(4)L(2)]X, where L = 4-(t)BuC(5)H(4)N (1b), C(5)H(5)N (2b), and THF (3b); X = PF(6)(-) (1b and 3b) and OTf(-) (2b). In 1b-3b, four mu-1,3 carboxylate ligands span relatively short Fe...Fe distances of 2.6633(11)-2.713(3) A. Intense (epsilon = 2700-3200 M(-1) cm(-1)) intervalence charge transfer bands were observed at 620-670 nm. EPR spectroscopy confirmed the S = (9)/(2) ground spin state of 1b-3b, the valence-delocalized nature of which was probed by X-ray absorption spectroscopy. The electron delocalization between paramagnetic metal centers is described by double exchange, which, for the first time, is observed in diiron clusters having no single-atom bridging ligand(s).
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Dongwhan
authors.initials: D
authors.lastname: Lee
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: DuBois
authors.forename: Brad
authors.initials: B
authors.lastname: Pierce
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hendrich
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
mesh_terms: D000465:Algorithms; D001665:Binding Sites; D002264:Carboxylic Acids / Q000737:chemistry*; D002384:Catalysis; D002412:Cations / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D058085:Iron Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D015394:Molecular Structure; D010084:Oxidation-Reduction
chemical_list: D002264:Carboxylic Acids; D002412:Cations; D058085:Iron Compounds; D008024:Ligands