Helmut Bertagnolli

Gold catalysis: in situ EXAFS study of homogeneous oxidative esterification.

Gold complexes were prepared and investigated as catalysts for the oxidative esterification of aldehydes. Stabilisation by pyridine ligands gave good conversions and the in situ extended X-ray absorption fine structure (EXAFS) study of the reactions indicated that the reaction mixtures contained only mononuclear gold species. Thus, this is the first proof for a homogeneous gold-catalysed oxidation reaction; the presence of nanoparticles could be excluded experimentally.

XAFS Spectroscopy of Liquid and Amorphous Systems: Presentation and Verification of a Newly Developed Program Package

A program package for XAFS data analysis, especially of liquid and amorphous samples, has been developed. For the first time a consequent error propagation is presented for all functions to be calculated in the course of the data analysis. The structural investigation of the Grignard compound CH3MgBr in diethyl ether is taken as an example for the various steps of the data analysis.

Raman microspectrometric identification of corrosion products formed on UO2 nuclear fuel during leaching experiments

Abstract The corrosion of directly disposed spent nuclear fuel by contact with intruding groundwater will alter the physical and chemical properties of this material. Secondary phases which formed during alteration of UO 2 surfaces were measured with Raman microspectrometry and the characteristic vibrational spectra of the materials were recorded. U phases were synthesized in hydrothermal autoclave syntheses. A Raman spectral library of UO 2 corrosion phases was set up for the identification of unknown products found on altered nuclear fuel samples. In a case study, U peroxide (UO 4 ) was identified by comparison with a natural sample as the main alteration phase by its characteristic O–O Raman vibration at 870 cm −1 . The results demonstrate the differentiation between UO 2 and its alteration products U(VI) oxyhydroxide and U(VI) peroxide (UO 4 ) on one sample with a relatively quick, non-destructive, spatially resolving measurement method which delivers oxidation state and molecular bonding information. Implications for the analysis of complex heterogenous matrices are discussed.

Investigations into the metal species of the homogeneous iron(III) catalyzed Michael addition reactions

An investigation into the species formed in the first step of the solvent free homogeneous Michael reaction of alpha,beta-unsaturated ketones with 2-oxocyclopentanecarboxylate (1) is presented. This reaction is catalyzed by FeCl(3).6H(2)O (2) and Fe(ClO(4))(3).9H(2)O (3). EXAFS, XANES, Raman and UV-Vis studies were carried out to explain the experimentally found higher catalytic activity of Fe(ClO(4))(3).9H(2)O (3) compared to FeCl(3).6H(2)O (2). A very intense pre-edge peak is found for a 1.6 mol% solution of FeCl(3).6H(2)O (2) in 1, suggesting a tetrachloroferrate(III) compound to be present in this solution. This is proved by UV-Vis and Raman spectroscopy. The counterion of this anionic complex is an octahedral [Fe(III)(1-H)(2)(H2O2)](+) complex with two deprotonated 2-oxocyclopentanecarboxylate (1) as the chelating ligand, (1-H)(-), as suggested by the examination of the XANES region, the obtained coordination numbers from the EXAFS analysis and by UV-Vis and Raman spectroscopies. In summary, the anion-cation species [Fe(III)Cl(4)](-)[Fe(III)(-H)(2)(H2O2)](+) is formed with FeCl(3).6H(2)O (2), whereas in the case of Fe(ClO(4))(3).9H(2)O (3) XAFS, Raman and UV-Vis investigations suggest the presence of a complex of the form [Fe(III)(1-H)(2)(H2O2)](+)[ClO(4)](-). The obtained results are discussed to explain the reduced catalytic activity of FeCl(3).6H(2)O (2) in comparison to Fe(ClO(4))(3).9H(2)O (3).

Experimental studies investigating the structure of soda-lime glasses after silver-sodium ion exchange

Abstract Structural rearrangements as a result of silver-sodium ion exchange have been investigated systematically on commercial soda-lime glasses by EXAFS experiments, X-ray diffraction, Fourier transform infrared spectroscopy, and density measurements. It was found that the atomic structure of the base glass is closely related to binary sodium silicates and that the addition of calcium causes a CaO bond length of ≌ 0.25 nm. Silver has been incorporated in an extended range of concentration (0.7 to 11 mol% Ag2O) well below the glass transformation temperature. Nevertheless, the typical silver environment consisting of two oxygens at an average distance of 0.215 nm was found. The second sphere around silver is dominated by an AgAg correlation at an approximately 0.298 nm spacing. Additionally, AgO and AgSi correlations have to be considered. The determined AgAg bond length indicates a d10-d10 interaction between silver ions. The so formed silver pairs or clusters should be precursory of the precipitation of crystalline silver particles at elevated temperatures. The interpretation of the difference function of diffraction data yields a pair correlation at 0.342 nm that can be ascribed to AgSi bond lengths. Comparing the EXAFS data at the Na and Ag K-edge structural relaxation is observed around the silver ions during low-temperature ion exchange although the glass volume remains constant in a wide range of composition. This relaxation entails essential consequences with respect to diffusion and conductivity behavior. Thus, it yields the structural basis of the mixed mobile effect in ion-exchanged glasses. The suggested memory effect means the inability of sodium to re-convert ‘silver-like’ sites below Tg which leads to local electric fields.

ω-Mercapto-functionalized hafnium- and zirconium-oxoclusters as nanosized building blocks for inorganic–organic hybrid materials: synthesis, characterization and photothiol-ene polymerization

Two isostructural mercapto-functionalized zirconium- and hafnium-oxoclusters [M12(μ3-O)8(μ3-OH)8(MP)24·n(MPA), MPA = HS–(CH2)2–C(O)OH; MP = HS–(CH2)2–C(O)O−; M= Zr, Hf; n = 4 for Zr, n = 5 for Hf] were prepared by reacting 3-mercaptopropionic acid with zirconium and hafnium butoxide, respectively, in an alkoxide : acid 1 : 7 molar ratio. The two oxoclusters Zr12 and Hf12, which are composed of two Zr6 and Hf6 sub-units bridged by four carboxylate ligands, were thoroughly characterized by single crystal X-ray diffraction, infrared spectroscopy (FT-IR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, thermogravimetry (TGA), differential thermoanalysis (DTA) and extended X-ray absorption spectroscopy (EXAFS). The zirconium oxocluster was then embedded in a polymethacrylic matrix by a photothiol-ene polymerization reaction by using different cluster : monomer molar ratios. EXAFS measurements performed on the polymethacrylic-based hybrid materials showed that the structure of the oxocluster is retained even after being embedded in the polymer matrix. Solid-state 13C NMR spectroscopy as well as FT-IR spectroscopy demonstrated that the inorganic–organic hybrid materials are characterized by an almost complete polymerization of methacrylic acid, in which the oxoclusters are embedded in and covalently bound to the polymer matrix.

The structure of liquid and supercritical deuterium fluoride from neutron scattering using high-pressure techniques

We present neutron diffraction data for deuterium fluoride at two liquid and four supercritical states in the temperature range of 300–473 K and for pressures up to 320 bar, spanning a factor of 4 in sample density. The intra- and intermolecular parts of the measured structure factors were separated and conclusions about the temperature and density dependence of the intra- and intermolecular structure are deduced.

Ab initio molecular dynamics simulation of hydrogen fluoride at several thermodynamic states

Liquid hydrogen fluoride is a simple but interesting system for studies of the influence of hydrogen bonds on physical properties. We have performed ab initio molecular dynamics simulations of HF at several thermodynamic states, where we examine the microscopic structure of the liquid as well as its static and dynamic properties. The results obtained show good agreement with well established data, and, moreover, we were able to show significant changes within the structure depending on the system’s temperature and density.

Spectroscopic set-up for simultaneous UV-Vis/(Q)EXAFS in situ and in operando studies of homogeneous reactions under laboratory conditions.

A novel experimental set-up for in operando studies of homogeneous catalyzed reactions under laboratory conditions has been developed and tested. It combines time-resolved X-ray absorption spectroscopy with UV/Vis spectroscopy. The reaction solution is stirred in a vessel and pumped in a circle by a peristaltic free gear-wheel through a measurement cell. The X-ray and UV/Vis beams probe the same sample volume of the cell orthogonally. Reactants can be added to the reaction mixture in the course of the measurements and a defined gas atmosphere can be adjusted up to a pressure of 10 bar. The in situ reduction of cerium(IV) ammonium nitrate to cerium(III) by isopropanol is studied as a test reaction with quick-XANES and UV/Vis measurements with a time resolution of 60 s and 1 s, respectively.

Transition metal oxide-doped mesostructured silica films

Abstract Mixed metal oxide-doped mesostructured silica films have been prepared by a combination of a ligand-assisted templating (LAT) and solvent evaporation-induced self-assembly (EISA) approach using metal alkoxides as precursors. To overcome the problem of the different hydrolysis and condensation rates of the various alkoxide precursors (silicon alkoxides and transition metal alkoxides), the hydrophilic head group of oligo(ethylene oxide) containing surfactants was coordinated to the M(OR) x groups resulting in metal-containing surfactants. These novel surfactants serve different functions in the EISA process: first, they moderate the hydrolysis and condensation rate of the transition metal alkoxide; second, they allow for a positioning of the transition metal alkoxide within the silica matrix; and third, they act as structure-directing agents. The obtained films are characterized by a high loading of the transition metal oxide species within the silica matrix and a homogeneous distribution throughout the whole film as shown by X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Several transition metal oxides have been incorporated into the silica matrix such as titania, zirconia and tantalum oxide.