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Distinct spectral features at the Fe L-edge of the two compounds K3[Fe(CN)6] and K4[Fe(CN)6] have been identified and characterized as arising from contributions of the ligand ð* orbitals due to metalto- ligand back-bonding. In addition, the L-edge energy shifts and total intensities allow changes in the ligand field and effective nuclear charge to be determined. It is found that the ligand field term dominates the edge energy shift. The results of the experimental analysis were compared to BP86 DFT calculations. The overall agreement between the calculations and experiment is good; however, a larger difference in the amount of ð back-donation between Fe(II) and Fe(III) is found experimentally. The analysis of L-edge spectral shape, energy shift, and total intensity demonstrates that Fe L-edge X-ray absorption spectroscopy provides a d...
New highly mixed phases have been identified in Cu/ZnO systems by EXAFS and XANES at both the Cu and Zn K-edge. The phases were generated by ball-milling Cu2O/ZnO mixtures under three different atmospheres of synthetic air (SA), SA + CO2 and CO2. The system milled in CO2 shows disproportionation of Cu2O into Cu0, Cu1+ (cuprite Cu2O-type phase) and Cu2+ (tenorite CuO-type phase), while most of the Zn2+ is transformed into a nanocrystalline/amorphous ZnO-type zincite that forms a superficial mixture of oxide and carbonate phases. When synthetic air is added to the CO2 atmosphere, ball milling results in the oxidation of nearly half the Cu1+ into Cu2+ with no Cu metal formed. The copper phase in this material is almost entirely amorphous. In SA, a significant amount of Cu2+- and Zn2+-based phases appears to react to form a nanocrystalline...
The long-term heat stabilisation efficiency of (natural) polyol additives in heavy metal- and zinc-free poly(vinyl chloride) (PVC) has been investigated. It is shown that polyols, such as sorbitol and xylitol, markedly reduce the dehydrochlorination rate and improve Congo Red values. Extraction experiments on unprocessed and ground-processed PVC-sorbitol (1.0 phr) mixtures after thermal degradation at 200 C revealed that especially in the ground-processed PVC-sorbitol system, sorbitol is partly converted into its mono- and dianhydro-derivatives 1,4-sorbitan and isosorbide, respectively. Apparently, the HCl released during thermal degradation acts as the catalyst. Similar intramolecular cyclodehydration reactions also occur with the natural polyols, erythritol and xylitol, under these conditions. Scrutiny of the measured dehydrochlorin...
NCN palladium(II) complexes have been covalently attached to the N- and C-termini of L-valine and to the N-terminus of the dipeptide L-Phe-L-Val-OMe. Remarkably, the hydrolysis of the NCN-Pd(II) L-Val-OMe compound afforded the corresponding palladated, free amino acid without affecting the metal site. This deprotected amino acid could be coupled to any protein, enzyme or peptidic chain by simple peptide chemistry. These bioorganometallic systems were active as catalysts in the aldol reaction between methyl isocyanate and benzaldehyde.
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