Karl-Heinz Hallmeier

XANES investigation of chemical states of nitrogen in polyaniline

Abstract X-ray absorption and photoelectron spectra of polyaniline were investigated in order to characterize the chemical bonding of its nitrogen atoms. The identification of neutral and charged nitrogen groups is of special interest. X-ray absorption near-edge structure (XANES) at the nitrogen K edge shows characteristic resonance structures reflecting transitions from the N1s core-level into unoccupied states. For comparison N1s X-ray photoelectron spectra were recorded representing the initial state of the N1s−12p( π ∗ σ ∗ ) transitions. Due to the increasing energy differences between the N1s initial state and the unoccupied π and σ states, discrete final states, originating from the different chemical bonding at the nitrogen atom (N, NH+  and NH), were resolved in the N K XANES.

Nitrogen K-shell excitations in complex molecules and polypyrrole

Abstract Experimental and theoretical studies of nitrogen K-shell near-edge absorption in complex compounds such as thiourea, benzalaniline, pyrrole, polypyrrole, tetraethylammonium, tetrabutylammonium and substituted 2-hydroxy-3-methoxy-benzyl-idene-aniline compounds were carried out. The quasi-atomic model was used in order to calculate the spectral distribution of oscillator strengths for transitions from the N 1s level to excited discrete and continuum states, to explain general trends in the changes of K-shell excitation spectra and to reveal their relationships with chemical bonding of the N atom in the compounds. The performed analysis of theoretical and experimental spectra evidences the central role of splitting of an intense N 1s −1 2p resonance in N K XANES formation in all compounds under study. The influence of the electronic charge transfer, bond conjugation and localization on the energies and intensities of π ∗ and σ ∗ resonances are discussed in detail. The strong connection between interference and chemical bonding effects on the main resonance features of X-ray absorption in the compounds under study is revealed.

Sulphur L2,3 and L1 XANES investigations of pyrite and marcasite

Abstract S L 2,3 and L 1 XANES of the polymorph minerals pyrite (FeS 2 ) and marcasite (two different cleavage planes) were measured in total electron yield mode using synchrotron radiation. Small but distinct differences were found in the fine structure of these spectra. Calculations with the FEFF-8 code were performed to reproduce the experimental data. Ex situ UV–ozone oxidation of the samples reveals different reactivity. Sulphate was identified on the pyrite and one marcasite cleavage planes whereas the second plane normal to the first one oxidises with changing quanta of sulphate and sulphite.

Metal chelates of N-benzothiazol-2-yl-, N-benzoxazol-2-yl- and N-(1H-benzimidazol-2-yl)-benzamide

Abstract The synthesis of the title ligands N-benzothiazol-2-yl-benzamide (1), N-benzoxazol-2-yl-benzamide (2) and N-(1H-benzimidazol-2-yl)-benzamide (3) is described. The molecular structure of 1 confirms the localization of a hydrogen atom at the nitrogen atom of the benzamide group. The ligands form 2:1 metal chelates under deprotonization with CuII, NiII, PdII and ZnII. 3 gives a cationic silver(I) complex. The complexes were characterized by XPS, NMR, and FAB mass spectroscopy. The molecular structure of two complexes was determined.

Characterization of the mercaptobenzothiazole bonding on cadmiumsulfide by MO interpretation of N K XANES results

The X-ray absorption near-edge structures (XANES) at the nitrogen K-edge of mercaptobenzothiazole (MBT), its anion, a chelate complex of this molecule, and its adsorbate on CdS(1010) exhibit distinct qualitative differences and characteristic peak shifts. It is shown that density functional theory (DFT) calculations of the respective systems in their electronic ground state can lead to an understanding of these spectral features. Their interpretation in terms of excitations into virtual molecular orbitals allows the assignment of the signals to functional groups in the chemical systems. By this means, the spectroscopic information on the adsorbate structure is confirmed and rationalized on a theoretical basis. It is deduced from the spectra that MBT is definitely adsorbed in its anionic form.

Angular-resolved XANES measurements of the polar and azimuthal orientation of alkanethiols on InP(110)

Abstract This Letter describes investigations of the X-ray absorption near-edge structure of adsorbed hexadecanethiol monolayers on InP(110). The angular (azimuthal and polar)-resolved measurements reveal the substrate-dependent tilt-angle of the alkyl C–C backbone (about 34° from normal). A unique feature observed on these monolayers is the nearly complete alignment of the alkyl chains with respect to the azimuthal orientation. We suggest that this adsorbate system represents the case of a single-domain organic monolayer. We interpret this behaviour, which deviates strongly from the well-known thiol films on gold, silver or copper, in terms of structural constraints and dangling-bond-induced pre-orientation of the alkanethiol chains.

Influence of zirconium phosphate on the properties of (VO)2P2O7 catalysts for the selective oxidation of n-butane to maleic anhydride

The effect of zirconium phosphate on the catalytic, textural and structural properties of (VO)2P2O7 catalysts has been studied. Catalysts with different P/V and Zr/V ratios were prepared using different preparation methods and characterized by thermo-analytical and texture measurements, X-ray diffraction (XRD), potentiometric titration, FTIR, X-ray absorption [X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)] and laser Raman spectroscopy. The n-butane conversion and the maxima of maleic anhydride (MA) yield shift to lower reaction temperatures on modification of (VO)2P2O7 with zirconium phosphate. There is no correlation between catalytic and textural properties of the modified catalysts. The zirconium phosphate modification causes a partial amorphization of the (VO)2P2O7 catalysts and leads to an enhancement of the VOPO4 microdomains (α1-, β-VOPO4 and amorphous VOPO4).

Splitting of the 1s−1 3p resonance in sulfur K XANES by surroundings in compounds with sulfurcarbon double bond

Abstract Results of the experimental and theoretical investigation of X-ray absorption S K near-edge structure in complex compounds containing a sulfurcarbon double bond mostly in the thioureato group are presented. In the framework of a quasi-atomic model the splitting of the 1s −1 3p resonance of the sulfur atom has been found to dominate the S K XANES. The splitting of this resonance into three (one π* and two σ*) components allows to explain the main features in the spectral density of oscillator strengths of transitions from the S K-shell. To describe the splitting both the resonance effects inside the SCN 2 group and the influence of atoms located in opposition to the sulfur atom have to be taken into account. Applying the quasi-atomic approximation the variation of the partial charge on the sulfur atom in the compounds is analyzed.

Inductive effect of methyl groups on acidopentaaminecobalt(III) complexes

Abstract Electron spectroscopy for chemical analysis (ESCA) was performed for [Co(NH3)5Cl](ClO4)2, trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2, [Co(NH2CH3)5Cl](ClO4)2 and trans-[Co(NH3)4(NH2CH3)(OSO3)](ClO4) complexes. Comparison of the results for the complexes [Co(NH3)5Cl](ClO4)2 and trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2 shows clearly the electronic influence (+I effect) of the methylamine group on the cobalt and through this on the chlorine atom in trans position. Comparison of [Co(NH2CH3)5Cl](ClO4)2 with trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2 shows that methylation of the four cis-NH3 ligands does not produce a proportional decrease in the binding energy of the cobalt atom, while the electron density of the chloro ligand is not affected. For the complex trans-[Co(NH3)4(NH2CH3)(OSO3)](ClO4) the +I effect is almost completely compensated by the presence of the sulfato group in trans position. Acid dissociation constants are also reported for [Co(NH3)5(OH2)]3+ and trans-[Co(NH3)4(NH2CH3)(OH2)]3+ ions. The implications of these results for the mechanism of the acid and base hydrolysis reactions of acidopentaaminecobalt(III) complexes are discussed. The preparation of the trans-[Co(NH3)4(NH2CH3)(OSO3)](ClO4) complex through the trans-[Co(NH3)4(NH2CH3)(SO3)]+ precursor is also described.

Molekülstruktur, elektrochemisches verhalten und NK XANES von 1,4-Bis(pyrrol-1-yl-carbonyl)benzol

ZusammenfassungDie Molekülstruktur und das cyclovoltammetrische Verhalten von 1,4-Bis-(pyrrol-1-yl-carbonyl)benzol (1) werden beschrieben. Das Röntgenabsorptionsspektrum von1 (NK XANES) wird bezüglich der N1s → π*-Übergänge im Vergleich mit 1H-Pyrrol untersucht.SummaryThe molecular structure and the cyclovoltammetric behaviour of 1,4-bis(pyrrol-1-yl-carbonyl)benzene (1) are described. The X-ray absorption spectrum of1 (NK XANES) is investigated with respect to the N1s → π* transitions in comparison with 1H-pyrrole.