Boris G. Shpeizer

X-Ray powder structure and Rietveld refinement of γ-zirconium phosphate, Zr(PO4)(H2PO4)·2H2O

A highly crystalline sample of γ-zirconium phosphate Zr(PO4)(H2PO4)·2H2O has been prepared by hydrothermal methods and its structure solved by X-ray powder diffractometry: monoclinic, space group P21, a= 5.3825(2), b= 6.6337(1), c= 12.4102(4)A, β= 98.687(2)° and Z= 2. The final agreement factors are: Rwp= 0.105, Rp= 0.079 and RF= 0.041. In the structure the metal atoms and one of the phosphate groups are located nearly in a plane. The octahedral co-ordination of the metal atom is completed by four oxygen atoms of the phosphate group and two oxygen atoms of the dihydrogenphosphate group. The remaining two oxygens of the dihydrogenphosphate group bind to protons and project into the interlayer space. These hydroxyl groups are hydrogen bonded to the water molecules. The water molecules reside in the pockets of these hydroxyl groups and are hydrogen bonded to each other to form a zigzag chain along the b axis.

Nickel oxide interstratified α-zirconium phosphate, a composite exhibiting ferromagnetic behavior

As part of an ongoing research program to synthesize novel pillared layered materials, nickel and cobalt hydroxyacetates were inserted between the layers of amine intercalates of α-zirconium phosphate. The structure of the resultant nickel composite, derived from x-ray powder data, was found to consist of a three-tiered layer of nickel atoms bridged by hydroxo and acetato groups. Heating to 420�C converted the hydroxyacetate layers to oxide and imparted ordered magnetic domains to the composite. The phosphate layers appear to act as a template directing the growth of the inserted layers in this class of composite materials.

On 29Si NMR relaxation as a structural criterion for studying paramagnetic supermicroporous silica-based materials: Silica-based materials incorporating Mn2+ ions into the silica matrix of SiO2–Al2O3–MnO

Supermicroporous paramagnetic materials SiO(2)-Al(2)O(3)-MnO and SiO(2)-MnO with different manganese concentrations have been probed by solid-state (29)Si NMR and magnetic susceptibility measurements. The (29)Si T(1) and T(2) experiments, performed in static and spinning samples, have resulted in determination of electron relaxation times, providing, in turn, quantitative interpretations of (29)Si T(1) times in terms of distances Mn-Si. The NMR relaxation data have revealed (29)Si T(1) time distributions, which are close to Gaussian and observed as different T(1) values obtained in MAS NMR experiments for isotropic (29)Si resonances and their sidebands. Such (29)Si T(1) distributions, being a common phenomenon in paramagnetic silica-based materials, can be however masked by the bulk magnetic susceptibility (BMS) effects increasing with concentrations of paramagnetic centers. The presence of T(1) distributions, in itself, is not a criterion for incorporation of paramagnetic ions into the silica matrix or its surface. However, a quantitative analysis of the experimentally-observed short (29)Si T(1) components, based on the well-determined electron relaxation times, can provide such a criterion.

New families of supermicroporous metal oxides: the link between zeolites and mesoporous materials.

Sol-gel hydrolysis reactions in propanol of two or more metal acetates or alkoxides in n-alkylamines have been found to yield porous mixed oxides with the presence of pores largely in the 10-20 A region.

Formation of Ni/NiO Nanoparticles in Supermicroporous Silica-Based SiO2-Al2O3-NiO Materials: Structural and Magnetic Studies

Microporous silica-based materials SiO2-Al2O3-NiO with a predominant pore size in the range 8-20 Aring, prepared by the sol-gel method by variation in Ni2+ concentrations from 0 to 30 weight %, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy. The nature of the nickel centers has been studied by magnetic susceptibility measurements supported by the XPS and X-ray experiments. It has been shown that these centers represent NiO and Ni0 (observed at high nickel loadings) aggregated into nanoparticles. The Ni0 nanoparticles are responsible for the room-temperature ferromagnetic behavior of the materials prepared with high nickel loadings.