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Extended X-ray absorption fine structure
About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.
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TL;DR: In this article, molecular clusters of rhodium were synthesized in the cages of NaY zeolite by decarbonylating supported Rhodium carbonyls, which were predominantly [Rh6(CO)16] prepared by carbonylation of adsorbed [Rh(CO 2(acac)] at 125 °C.
Abstract: Molecular clusters of rhodium were synthesized in the cages of NaY zeolite by decarbonylating supported rhodium carbonyls, which were predominantly [Rh6(CO)16] prepared by carbonylation of adsorbed [Rh(CO)2(acac)] at 125 °C. The samples were characterized by infrared and X-ray absorption fine structure spectroscopies. [Rh6(CO)16] formed at 125 °C, with a higher yield observed for the clusters in the uncalcined zeolite than for those in the calcined zeolite. Rhodium clusters formed by decarbonylation of [Rh6(CO)16] in calcined NaY zeolite in the presence of He at temperatures of 200, 250, or 300 °C were characterized by Rh−Rh coordination numbers of approximately 3.7, indicating that the octahedral metal frame of the [Rh6(CO)16] precursor remained nearly intact. When the decarbonylation of [Rh6(CO)16] took place in the presence of H2, partially decarbonylated rhodium clusters formed at 200 °C, having a Rh−Rh coordination number of about 3.6. Higher-temperature treatments in H2 resulted in the sintering of ...
70 citations
TL;DR: Metal–organic layers stabilize FeII or CoII-terpyridine diradical complexes to catalyze alkylazide Csp3–H amination and benzylic C–H borylation, respectively.
Abstract: We report the synthesis of a terpyridine-based metal-organic layer (TPY-MOL) and its metalation with CoCl2 and FeBr2 to afford CoCl2·TPY-MOL and FeBr2·TPY-MOL, respectively. Upon activation with NaEt3BH, CoCl2·TPY-MOL catalyzed benzylic C-H borylation of methylarenes whereas FeBr2·TPY-MOL catalyzed intramolecular Csp3 -H amination of alkyl azides to afford pyrrolidines and piperidines. X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy, UV-Vis-NIR spectroscopy, and electron paramagnetic spectroscopy (EPR) measurements as well as density functional theory (DFT) calculations identified M(THF)2·TPY-MOL (M = Co or Fe) as the active catalyst with a MII-(TPY˙˙)2- electronic structure featuring divalent metals and TPY diradical dianions. We believe that site isolation stabilizes novel MII-(TPY˙˙)2- (M = Co or Fe) species in the MOLs to endow them with unique and enhanced catalytic activities for Csp3 -H borylation and intramolecular amination over their homogeneous counterparts. The MOL catalysts are also superior to their metal-organic framework analogs owing to the removal of diffusion barriers. Our work highlights the potential of MOLs as a novel 2D molecular material platform for designing single-site solid catalysts without diffusional constraints.
70 citations
TL;DR: Fitting of the EXAFS data has confirmed the existence of a vanadium-vanadium interaction between two different V2O5 layers and an oxygen bridge between them and focused attention along the z axis.
Abstract: Polarized X-ray absorption spectroscopy has been used to study the short-range structure of deposited films of V2O5 xerogel. The material is characterized by a layer of VO5 units with the V−O apical bond perpendicular to the basal (xy) plane. We have focused our attention along the z axis. Experiments were carried out by extended X-ray absorption fine structure (EXAFS) spectroscopy in a grazing incidence geometry and showed evidence for close interactions between neighboring layers of V2O5. The structure is described by two sheets of V2O5 facing each other. Fitting of the EXAFS data has confirmed the existence of a vanadium−vanadium interaction between two different V2O5 layers and an oxygen bridge between them.
70 citations
TL;DR: In this article, the utility of in situ X-ray absorption spectroscopy (XAS) in determining structural parameters, through analysis of the extended Xray absorption fine structure (EXAFS), and electronic perturbations, through a white line analysis of XAS near edge structure (XANES), is demonstrated for Pt/C, PtRu/C and PtMo/C fuel cell electrodes.
70 citations
TL;DR: In this paper, the results of the authors recent studies on several states of the MoFe protein and its FeMo cofactor (which is extruded by treatment with N-methylformamide).
Abstract: Nitrogenase is a complex bacterial enzyme system that is responsible for the conversion of atmospheric N/sub 2/ to ammonia. The structure and function of molybdenum in the MoFe protein of this system has been the subject of a number of investigations, including the use of X-ray absorption spectroscopy. This paper reports the results of the authors recent studies on several states of the MoFe protein and its FeMo cofactor (which is extruded by treatment with N-methylformamide). Mo K-edge (XANES) and extended fine structure (EXAFS) spectra have been recorded to high energies above the absorption edge with excellent signal-to-nose on the semireduced form of the MoFe protein from both Clostridium pasteurianum and Azotobacter vinelandii and on the as isolated FeMo-co and FeMo-co treated with benzenethiol and with benzeneselenol. In all of the states studied, EXAFS results reveal that the Mo is in an environment that contains two or three oxygen (or nitrogen) atoms at 2.10-2.12 A, three to five S atoms at 2.37 A, and three to four Fe atoms at 2.68-2.70 A. The numbers of these ligands change upon removal of the cofactor from the protein as discussed in the paper. For FeMo-co, comparisons also show that thil/selenol is notmore » binding directly to the Mo site. The results of these EXAFS (and their XANES published earlier) definitely show the presence of several low-Z ligands and are not compatible with a tetrahedral arrangement of only nearest S neighbors at the Mo site.« less
70 citations