XANES Characterization of Extremely Nanosized Metal-Carbonyl Subspecies (Me = Cr, Mn, Fe, and Co) Confined into the Mesopores of MCM-41 Materials

Abstract

A study of the stability, local order, and interaction of the surface silanol groups of MCM-41 with transition metal carbonyls M x (CO) y (where M = Cr, Mn, Fe, Co) introduced by a chemical alternative method was performed by X-ray absorption near-edge spectroscopy (XANES). These molecular species, catalytically active for ethylene polymerization reactions, were previously characterized by FTIR and NMR in order to confirm their monodispersion and confined location into the mesopores of the MCM-41 material. Present experimental results indicate the high dispersion of metal species in all cases. Symmetry and stability depend on type of compound, Fe-carbonyl having the lowest stability. Changes in metal coordination and oxidation state are clearly followed by XANES indicating the interaction between sub-carbonyl species and the walls of the mesopores.

X-ray absorption spectroscopic and magnetic characterization of cobalt-doped zinc oxide nanocrystals prepared by the molten-salt method

“…Therefore, this feature gains significant spectral weight for the case of noncentrosymmetric tetrahedral geometry of an absorbing atom through the mixing of d-p orbitals. In fact, an intense feature P was reported for Co 2 (CO) 8 in which four CO molecules surround the cobalt atom [17]. On the contrary, the present spectrum of CoO with the rocksalt structure shows only a weak pre-edge peak P due to the octahedral symmetry of cobalt ion.…”

Molten salt-assisted synthesis of bulk CoOOH as a water oxidation catalyst

“…It can be observed that the line shapes of Co K -edge XANES spectra for CoOOH-650, CoOOH-750, and CoOOH-850 catalyst are very analogous, presenting that the electronic structure and the local structure of cobalt ions are not changed. The position of the adsorption edge reflects the oxidation state of the cobalt ion [35] , namely that the absorption-edge positions in CoOOH-650 and CoOOH-750 are very different with the references, suggesting that the oxidation state of cobalt ions is Co (III) [36] , while the position of the adsorption edge of CoOOH-850 shifts slightly to the left, indicating that the cobalt valence has decreased slightly. Furthermore, the white line of CoOOH-750 has the highest intensity, indicating that it has a higher symmetry.…”

Spectroscopic X-ray and Mössbauer Characterization of M6 and M5 Iron(Molybdenum)-Carbonyl Carbide Clusters: High Carbide-Iron Covalency Enhances Local Iron Site Electron Density Despite Cluster Oxidation

“…The calculated isomer shift trend observed for the complexes agrees with the “counter-intuitive” trend previously discussed for iron carbonyls, in which the more formally oxidized complex (e.g., 2 ) has a higher average isomer shift. 51−53 The DFT calculated δ parameter for the individual iron sites yields a consistent pattern that allows us to separate them into two groups: those with semibridging (group B) and without bridging CO ligands (group NB). The NB irons are consistently more reduced than B irons, indicating that the geometric distortion induced by a bridging CO allows for more efficient π-backbonding.…”