scholarly journals Operando XANES from first-principles and its application to iridium oxide

2020 ◽  
Vol 22 (19) ◽  
pp. 10807-10818 ◽  
Author(s):  
Francesco Nattino ◽  
Nicola Marzari
Keyword(s):  
Density Functional Theory ◽  
Absorption Spectra ◽  
First Principles ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Applied Potential ◽  
Functional Theory ◽  
X Ray ◽  
Continuum Description ◽  
X Ray Absorption

Density-functional theory calculations augmented with a continuum description of the electrochemical environment are implemented to simulated X-ray absorption spectra as a function of the applied potential.

scholarly journals Copper-catalyzed aerobic oxidative coupling: From ketone and diamine to pyrazine

2015 ◽  
Vol 1 (9) ◽  
pp. e1500656 ◽  
Author(s):  
Kun Wu ◽  
Zhiliang Huang ◽  
Xiaotian Qi ◽  
Yingzi Li ◽  
Guanghui Zhang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Oxidative Coupling ◽  
Density Functional ◽  
Coupling Reaction ◽  
Density Functional Theory Calculations ◽  
Radical Species ◽  
Functional Theory ◽  
X Ray ◽  
Oxidative Coupling Reaction ◽  
X Ray Absorption

Copper-catalyzed aerobic oxidative C–H/N–H coupling between simple ketones and diamines was developed toward the synthesis of a variety of pyrazines. Various substituted ketones were compatible for this transformation. Preliminary mechanistic investigations indicated that radical species were involved. X-ray absorption fine structure experiments elucidated that the Cu(II) species 5 coordinated by two N atoms at a distance of 2.04 Å and two O atoms at a shorter distance of 1.98 Å was a reactive one for this aerobic oxidative coupling reaction. Density functional theory calculations suggested that the intramolecular coupling of cationic radicals was favorable in this transformation.

Solid energy calibration standards for PK-edge XANES: electronic structure analysis of PPh4Br

2018 ◽  
Vol 25 (2) ◽  
pp. 529-536 ◽  
Author(s):  
Anastasia V. Blake ◽  
Haochuan Wei ◽  
Courtney M. Donahue ◽  
Kyounghoon Lee ◽  
Jason M. Keith ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Energy Calibration ◽  
Functional Theory ◽  
Calibration Standards ◽  
X Ray ◽  
X Ray Absorption ◽  
Edge Feature

PK-edge X-ray absorption near-edge structure (XANES) spectroscopy is a powerful method for analyzing the electronic structure of organic and inorganic phosphorus compounds. Like all XANES experiments, PK-edge XANES requires well defined and readily accessible calibration standards for energy referencing so that spectra collected at different beamlines or under different conditions can be compared. This is especially true for ligandK-edge X-ray absorption spectroscopy, which has well established energy calibration standards for Cl (Cs2CuCl4) and S (Na2S2O3·5H2O), but not neighboring P. This paper presents a review of common PK-edge XANES energy calibration standards and analysis of PPh4Br as a potential alternative. The PK-edge XANES region of commercially available PPh4Br revealed a single, highly resolved pre-edge feature with a maximum at 2146.96 eV. PPh4Br also showed no evidence of photodecomposition when repeatedly scanned over the course of several days. In contrast, we found that PPh3rapidly decomposes under identical conditions. Density functional theory calculations performed on PPh3and PPh4+revealed large differences in the molecular orbital energies that were ascribed to differences in the phosphorus oxidation state (IIIversusV) and molecular charge (neutralversus+1). Time-dependent density functional theory calculations corroborated the experimental data and allowed the spectral features to be assigned. The first pre-edge feature in the PK-edge XANES spectrum of PPh4Br was assigned to P 1s → P-C π* transitions, whereas those at higher energy were P 1s → P-C σ*. Overall, the analysis suggests that PPh4Br is an excellent alternative to other solid energy calibration standards commonly used in PK-edge XANES experiments.

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