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Assignment of Pre-edge Features in the Ru K-edge X-ray Absorption Spectra of Organometallic Ruthenium Complexes.

ABSTRACT: The nature of the lowest energy bound-state transition in the Ru K-edge X-ray Absorption Spectra for a series of Grubbs-type ruthenium complexes was investigated. The pre-edge feature was unambiguously assigned as resulting from formally electric dipole forbidden Ru 4d<--1s transitions. The intensities of these transitions are extremely sensitive to the ligand environment and the symmetry of the metal centre. In centrosymmetric complexes the pre-edge is very weak since it is limited by the weak electric quadrupole intensity mechanism. By contrast, upon breaking centrosymmetry, Ru 5p-4d mixing allows for introduction of electric dipole allowed character resulting in a dramatic increase in the pre-edge intensity. The information content of this approach is explored as it relates to complexes of importance in olefin metathesis and its relevance as a tool for the study of reactive intermediates.

SUBMITTER: Getty K

PROVIDER: S-EPMC2819416 | biostudies-literature | 2008 Mar

REPOSITORIES: biostudies-literature

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Assignment of Pre-edge Features in the Ru K-edge X-ray Absorption Spectra of Organometallic Ruthenium Complexes.

Getty Kendra K Delgado-Jaime Mario Ulises MU Kennepohl Pierre P

Inorganica chimica acta 20080301 4

The nature of the lowest energy bound-state transition in the Ru K-edge X-ray Absorption Spectra for a series of Grubbs-type ruthenium complexes was investigated. The pre-edge feature was unambiguously assigned as resulting from formally electric dipole forbidden Ru 4d<--1s transitions. The intensities of these transitions are extremely sensitive to the ligand environment and the symmetry of the metal centre. In centrosymmetric complexes the pre-edge is very weak since it is limited by the weak ...[more]

PMID: 20151030

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Project description:Mn K-edge X-ray absorption spectroscopy (XAS) was used to gain insights into the geometric and electronic structures of [Mn(II)(Cl)2(Me2EBC)], [Mn(IV)(OH)2(Me2EBC)](2+), and [Mn(IV)(O)(OH)(Me2EBC)](+), which are all supported by the tetradentate, macrocyclic Me2EBC ligand (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). Analysis of extended X-ray absorption fine structure (EXAFS) data for [Mn(IV)(O)(OH)(Me2EBC)](+) revealed Mn-O scatterers at 1.71 and 1.84 Å and Mn-N scatterers at 2.11 Å, providing the first unambiguous support for the formulation of this species as an oxohydroxomanganese(IV) adduct. EXAFS-determined structural parameters for [Mn(II)(Cl)2(Me2EBC)] and [Mn(IV)(OH)2(Me2EBC)](2+) are consistent with previously reported crystal structures. The Mn pre-edge energies and intensities of these complexes were examined within the context of data for other oxo- and hydroxomanganese(IV) adducts, and time-dependent density functional theory (TD-DFT) computations were used to predict pre-edge properties for all compounds considered. This combined experimental and computational analysis revealed a correlation between the Mn-O(H) distances and pre-edge peak areas of Mn(IV)?O and Mn(IV)-OH complexes, but this trend was strongly modulated by the Mn(IV) coordination geometry. Mn 3d-4p mixing, which primarily accounts for the pre-edge intensities, is not solely a function of the Mn-O(H) bond length; the coordination geometry also has a large effect on the distribution of pre-edge intensity. For tetragonal Mn(IV)?O centers, more than 90% of the pre-edge intensity comes from excitations to the Mn?O ?* MO. Trigonal bipyramidal oxomanganese(IV) centers likewise feature excitations to the Mn?O ?* molecular orbital (MO) but also show intense transitions to 3dx(2)-y(2) and 3dxy MOs because of enhanced 3d-4px,y mixing. This gives rise to a broader pre-edge feature for trigonal Mn(IV)?O adducts. These results underscore the importance of reporting experimental pre-edge areas rather than peak heights. Finally, the TD-DFT method was applied to understand the pre-edge properties of a recently reported S = 1 Mn(V)?O adduct; these findings are discussed within the context of previous examinations of oxomanganese(V) complexes.

Dataset Information

Assignment of Pre-edge Features in the Ru K-edge X-ray Absorption Spectra of Organometallic Ruthenium Complexes.

Publications

Assignment of Pre-edge Features in the Ru K-edge X-ray Absorption Spectra of Organometallic Ruthenium Complexes.

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