ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Crystal structural characterization of the Sr8Ga16Ge30 compound was carried out with the Rietveld refinement method using x-ray powder diffraction data. The structure corresponds to that of the type-I clathrate hydrate, with the Sr atoms filling the “cages” formed by the Ga and Ge atoms. Anisotropic displacement parameters were refined. The limiting figure for rms values of the Sr(1) atoms enclosed in the dodecahedral cages is a sphere, while that for the Sr(2) atoms in the tetrakaidecahedral cages move is an oblate ellipsoid. A comparison of the sizes of the cages in this structure with the ones in other M8GaxGe46−x (M=K, Ba, or void) structures shows that once the structure is filled (i) there is very little variation in size of the tetrakaidecahedral cages and (ii) the dodecahedral cages expand only slightly (measurably) as a function of the filler size. This is an important result from the thermoelectric point of view because it means that once the structure is full, the cages will not “close over” the guests, limiting their movement and, thus, raising the thermal conductivity. The melting point of Sr8Ga16Ge30 is approximately 765 °C and the apparent optical gap is 0.05 eV.

Via a direct reaction of NbAsO 5 and ACl (A ) Rb, Cs), a new family of layered niobium(V) arsenate compounds, ANbAsO 5 Cl, was synthesized. Single crystals of these new phases were grown by employing either a single flux of the respective chloride or a eutectic flux of ACl/A′Cl (A′ ) Na, K). The cell constants are a ) 6.6605(6) Å, c ) 7.680(2) Å for RbNbAsO 5 Cl (Z ) 2, tetragonal, P4/n); a ) 6.662(2) Å, b ) 7.879(3) Å, c ) 6.663(1) Å, β ) 90.01(2)°for CsNbAsO 5 Cl (Z ) 2, monoclinic, P2/n). The single-crystal X-ray structures show that the title compounds adopt a layered framework that consists of alternately stacked NbAsO 5 slabs and (100) ACl rock salt sheets. The Nb 5+ cation resides in a distorted [5+1] NbO 5 Cl octahedral coordination environment. The formation of a layered structure can be envisioned if the NbAsO 5 framework is chemically dissected by molten alkali-metal chloride along the planes of long (weak) Nb-O bonds. Topologically, the Clanions insert into a three-dimensional framework to replace the long Nb-O bonds (2.23 Å) by coordination intercalation. The [NbAsO 5 Cl] slab adopts the polyhedral arrangement of the single [NbAsO 5 ] slab found in the monoclinic R-NbAsO 5 phase. The chloride capped niobium arsenate anionic slab [NbAsO 5 Cl]is neutralized by the countercation A + . This paper reports the synthesis, structure, and UV-vis diffuse reflectance spectroscopy of the title compounds.

Nonaniobium arsenic pentacosaoxide contains 3 × 3 ReO3-type NbO~, octahedral columns extended along c. Each column is linked to four crystallographically identical columns through shared edges of NbO6 octahedra and shared corners of AsO4 tetrahedra.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.