Bestimmung der Art der Wasserbindung im Xonotlit 6 CaO-6 SiO2-H2O

The ¹H-NMR spectra of powdered synthetic xonotlite (5.64 CaO · 6SiO₂ · 1.56 H₂O) at +22 and ?150°C have been recorded. From the line shape the various bonding states of the protons are determined. Per 6 SiO₂ units, 1.46 H₂O are bound in form of OH groups and 0.20 H₂O exist at room temperature as mobile water molecules. By quantitative evaluation it is shown, that the constitution of the examined sample has to be represented by the formula (CaOH)_2.0Ca_3.6(H_0.8Si₆O₁₇). 0.2 H₂O. Line shape analysis provides the possibility to distinguish between CaOH and SiOH protons. The proton-proton distances are calculated, and by comparison with the known X-ray data the positions of the CaOH protons are proposed.     

31P MAS-NMR an Phosphoroxidsulfiden — experimentelle Bestimmung und quantenchemische Berechnung der Tensoren der chemischen Verschiebung

³¹P MAS-NMR of Phosphorus Oxide Sulfides — Experimental Determination and Quantumchemical Calculation of Chemical Shift Tensors By high resolution solid state ³¹P MAS NMR and analysis of spinning sidebands the principal values of the chemical shift tensors in the series P₄O₆S_n with n = 0–4 have been determined. The orientations of the corresponding principal axes within the molecules have been derived. All magnetic shielding tensors show axial symmetry within the limits of experimental error. Thus the orientation of the shielding tensor within the molecules can be deduced indirectly. This information is usually not accessible for polycrystalline samples. The principal values of the tensor of the trivalent phosphorus atoms in P₄O₆S seem to deviate considerably from those of the other compounds with respect to anisotropy and axiality. The reason is a dynamic effect: the rotation of the molecule about the PS bond. All experimental results are confirmed by ab-initio calculations using the IGLO method.     

Hochauflösende Festkörper-NMR-Untersuchungen an Kieselsäuren. I. Hochauflösende 29Si-Festkörper-NMR-Untersuchungen an polykristallinen Phyllokieselsäuren (H2Si2O5)x bei tiefem und hohem Magnetfeld

Solid-State High Resolution N.M.R. Studies of Silicic Acids. I. Solid-State High Resolution ²⁹Si N.M.R. Studies of Polycrystalline Phyllosilicic Acids (H₂Si₂O₅)_x at Low and High Magnetic Fields ²⁹Si NMR studies of two samples of phyllosilicic acid show that these samples represent two phases of (H₂Si₂O₅)_x, which can be distinguished by the different isotropic values of the chemical shift, while the amounts and the signs of the anisotropy of their ²⁹Si-shielding tensors agree. The sample A (α-phase) consists of a pure phyllosilicic acid with a regular layer structure, while the sample B (δ-phase) is characterized as a phyllosilicic acid with partial high-condensed areas. From N.M.R. data a model is deduced to describe the structure of this sample. The field-dependence of the line widths for both phases leads to the conclusion that in phyllosilicic acids a distribution of the structural parameters of the SiO₄ tetrahedrons appears. The discussion of the shielding anisotropy data of both (H₂Si₂O₅)_x phases suggests a picture of the crystal structures, which is in disagreement with the known crystal structure of (H₂Si₂O₅)_x-I.     

Polarization analysis in soft X‐ray diffraction to study magnetic and orbital ordering

An experimental approach to the analysis of charge, magnetic and orbital ordering in 3d transition‐metal oxides is presented. The technique combines two important components: azimuthal rotations around the Bragg wavevector and polarization analysis of the Bragg intensities in the range 500–900 eV. The polarization analysis is performed using graded multilayers, which are translated and rotated in the vacuum chamber. It is shown why these two components are important to determine the origin of the Bragg scattered signals and how they allow us to separate the different contributions. Examples are given for the oxygen K and the Mn, Co, Ni and Cu L_2,3‐edges, and the advantages and drawbacks of this experimental technique are discussed.     

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