Ursula Wilczok

Hollow mesoporous silica fibers: tubules by coils of tubules

Hollow mesoporous silica fibers have been synthesized under acidic conditions in a two-phase static system. The fibers always have a circular internal architecture with hexagonally arranged channels running perpendicularly around the fiber axis. The inner radius of the hollow fibers is variable and the fibers are connected with solid fibers without inner cavity. This points to a novel formation mechanism for the central cavity of the hollow fibers.

Mg2OsH6 — A new ternary hydride with the K2PtCl6-type structure

Abstract A new ternary hydride with the composition Mg 2 OsH 6 has been synthesized from MgH 2 and osmium powder. The structure was determined, by Guinier-Hagg X-ray diffraction and neutron powder diffraction, to be of the K 2 PtCl 6 type with a cubic unit cell dimension of 6.6828(6) A. The Os-H bond length in the octahedral complex was refined from a neutron diffraction pattern of the deuteride Mg 2 OsD 6 to a value of 1.68(1) A.

A new pathway to Mg2Ni and an MgNi carbide

Abstract Bis(η 3 -allyl) nickel compounds react with catalytically prepared magnesium hydride (molar ratio, 1:2) in tetrahydrofuran at room temperature to give propene and finely divided (surface areas, about 100 m 2 g −1 ) amorphous solids. On heating (400 °C) followed by hydrogenation-dehydrogenation these are converted into crystalline Mg 2 Ni. Mg 2 Ni prepared by this method can be hydrogenated at 200 °C under normal pressure. Bis(η 3 -allyl) nickel reacts with magnesium hydride (molar ratio, 1:1) or with hydridomagnesiumchloride (molar ratio, 1:2) under the same conditions to give amorphous solids having the composition MgNiC x H y , x = 1.2–1.8, y = 2.3–3.4. At 690 °C this solid is converted into a crystalline product which, on the basis of hydrogenation-dehydrogenation experiments and X-ray powder analysis, is suggested to be a mixture of Mg 2 Ni, the known carbide MgNi 3 C x and MgO.

1H NMR signal broadening in spectra of alkane molecules adsorbed on MFI-type zeolites

The anisotropic behavior of C1-C6 alkane molecules adsorbed in MFI zeolite was studied by 1H nuclear magnetic resonance (NMR) using single-pulse excitation, Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, Hahn echo (HE) pulse sequence, and magic-angle spinning. The molecular order parameter was obtained by both static 2H NMR spectroscopy and molecular simulations. This yields an order parameter in the range of 0.28-0.42 for linear alkanes in MFI zeolite, whereas the parameter equals zero for FAU zeolite with a cubic symmetry. Thus, in the case of a zeolite with a non-cubic symmetry like MFI, the mobility of the molecules in one crystallite cannot fully average the dipolar interaction. As a consequence, transverse nuclear magnetization as revealed in the echo attenuation notably deviates from a mono-exponential decay. This information is of particular relevance for the performance of pulsed field gradient (PFG) NMR diffusion experiments, since the occurrence of non-exponential magnetization attenuation could be taken as an indication of the existence of different molecules or of molecules in different states of mobility.

Structural analysis of a novel carbon stabilized MgPd alloy: Mg2PdCx

Abstract The novel crystalline MgPd alloy, M2PdCx, was initially isolated through dehydrogenation of an amorphous hydride, Mg2PdCxH2 prepared using solution techniques. Further work showed that Mg2PdCx could also be obtained by heating Mg and Pd metals in the presence of graphite. The carbide crystallizes with a cubic unit cell a = 12.0480(4) A in space group Fd 3 m (227). The X-ray powder pattern could be refined on the basis of a Ti2Ni structural model with a final RF value of 0.047 for the metal atom substructure, Mg2Pd. Although the carbon atom position could not be refined, samples prepared by high temperature techniques indicated that the carbon content,x, can be as low as x = 0.1.