title: X-ray absorption spectroscopy and density functional theory studies of [(H3buea)FeIII-X]n- (X = S2-, O2-, OH-): comparison of bonding and hydrogen bonding in oxo and sulfido complexes.
abstract: Iron L-edge, iron K-edge, and sulfur K-edge X-ray absorption spectroscopy was performed on a series of compounds [Fe(III)H(3)buea(X)](n-) (X = S(2-), O(2-), OH(-)). The experimentally determined electronic structures were used to correlate to density functional theory calculations. Calculations supported by the data were then used to compare the metal-ligand bonding and to evaluate the effects of H-bonding in Fe(III)(-)O vs Fe(III)(-)S complexes. It was found that the Fe(III)(-)O bond, while less covalent, is stronger than the Fe(III)(-)S bond. This dominantly reflects the larger ionic contribution to the Fe(III)(-)O bond. The H-bonding energy (for three H-bonds) was estimated to be -25 kcal/mol for the oxo as compared to -12 kcal/mol for the sulfide ligand. This difference is attributed to the larger charge density on the oxo ligand resulting from the lower covalency of the Fe-O bond. These results were extended to consider an Fe(IV)(-)O complex with the same ligand environment. It was found that hydrogen bonding to Fe(IV)(-)O is less energetically favorable than that to Fe(III)(-)O, which reflects the highly covalent nature of the Fe(IV)(-)O bond.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Dey
authors.forename: Rosalie K
authors.initials: RK
authors.lastname: Hocking
authors.forename: Peter
authors.initials: P
authors.lastname: Larsen
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Borovik
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D015502:Absorptiometry, Photon; D005290:Ferric Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D013455:Sulfur; D010100:Oxygen