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Abstract: Two new alkali-metal tin(II) phosphates – Na10Sn31(HPO4)6(P2O7)6(PO4)12 (1) and K2SnP2O7 (2) – were synthesized by high-temperature reactions and structurally characterized by single-crystal X-ray diffraction. Na10Sn31(HPO4)6(P2O7)6(PO4)12 crystallized in the noncentrosymmetric space group P-62c (No. 190) with a =9.6445(1)Å, b =9.6445(1)Å, c =34.059(6)Å, V =2743.6(7)Å3 and Z =1. K2SnP2O7 crystallized in the monoclinic space group P21/n with a =9.856(3)Å, b =6.7244(1)Å, c =12.225(3)Å, β =108.240(5)°, V =769. 5(3)Å3 and Z =4. Both structures exhibit a novel open-framework structure. The crystal structure of 1 contains SnO3 and SnO4 polyhedra sharing corners with [HPO4]2−, [PO4]3− and [P2O7]4− groups, which form tunnels of six rings filled with Na+ cations and parallel to the c-axis, which are connected via O–Sn–O bridges to form a three-dimensional open framework. The crystal structure of 2 contains SnO4 seesaw polyhedra sharing corners with diphosphate groups to form a three-dimensional [SnP2O7]2− framework that exhibits a tunnel structure of 10- and 12-membered rings expanding along [011] and [100] with four arrays of K+ cations located in channels of the framework. [Copyright &y& Elsevier]

Abstract: A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)2− x (MoO4) x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the 5 D 0→7 F 2 emission of Eu3+ activated at wavelength of 396nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the 5 D 0→7 F 2 transition. As the molybdate content increases the emission intensity of the 615nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO4)2− x (MoO4) x is investigated and discussed. [Copyright &y& Elsevier]

Abstract: Quaternary chalcogenides InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9 were synthesized on direct combination of their elements in stoichiometric ratios at T>800°C under vacuum. Their structures were determined with X-ray diffraction of single crystals. InSn2Bi3Se8 crystallizes in monoclinic space group C2/m (No. 12) with a=13.557(3)Å, b=4.1299(8)Å, c=15.252(3)Å, β=115.73(3)°, V=769.3(3)Å3, Z=2, and R1 /wR2 /GOF=0.0206/0.0497/1.092; In0.2Sn6Bi1.8Se9 crystallizes in orthorhombic space group Cmc21 (No. 36) with a=4.1810(8)Å, b=13.799(3)Å, c=31.953(6)Å, V=1843.4(6)Å3, Z=4, and R1/wR2/GOF=0.0966/0.2327/1.12. InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9 are isostructural with CuBi5S8 and Bi2Pb6S9 phases, respectively. The structures of InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9 feature a three-dimensional framework containing slabs of NaCl-(311) type with varied thicknesses. Calculations of the electronic structure and measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps. Both compounds show n-type semiconducting properties with Seebeck coefficients −270 and −230μV/K at 300K for InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9, respectively. [Copyright &y& Elsevier]

Abstract: CeO2 nanocrystals of cubic and rod shape have been synthesized under hydrothermal conditions on controlling the pH, temperature and duration of reaction. High-resolution transmission electron microscopy indicates that exposed crystal planes are {110} and {100} for rods but {100} for cubes. These nanocrystals have been used in the preparation of a Rh/CeO2 catalyst on an Al2O3 support to test the catalytic activity for ethanol reforming. These catalysts as prepared show good H2 selectivity compared to catalysts with irregular CeO2 nanoparticles. The {100}/{110}-dominant surface structures play a crucial role in enhancing ethanol reforming; this reaction is important for fuel-cell applications. [Copyright &y& Elsevier]

Ternary chalcogenides, GeSb 2 Se 3 and Ge 3 Sb 4 Se 7 , were synthesized and characterized. These chalcogenides are the first ternary selenides in a ternary Ge-Sb-Se system that feature a layer structure related to black phosphorus and SnSe-type structures. Both compounds contain a ∞ 1 [Sb 2 Se 2 ] 2- unit with Sb + cations in a zigzag Sb-Sb chain structure, and Sb 3+ cations in a distorted NaCl 100 -type of ∞ 1 [Ge n -2 Sb 2 Se n ] 2+ unit ( n = 4, 5). These materials exhibit n-type semiconducting properties with thermal conductivity significantly lower than that of GeSe and Sb 2 Se 3 , which could be correlated to the 1D Sb + chain and disordered sites with different Ge/Sb compositions. It is anticipated that these newly discovered ternary chalcogenides may provide unique properties with enhanced thermoelectric properties.

Alkaline earth metal substitutions on the A-site of pyrochlore oxide M x La 2- x Ce 1.8 Ru 0.2 O 7- δ (M = Mg, Ca) were studied as catalyst materials for oxidative/autothermal steam reforming of ethanol (OSRE/ATR). The as-prepared oxides were synthesized by a combustion method and characterized using powder X-ray diffraction (PXRD), and X-ray photoelectron and absorption spectroscopy (XPS and XAS). PXRD Rietveld analysis and elemental analysis (ICP-AES) support the formation of a pyrochlore-type structure (space group Fd 3̄ m ) with a distorted coordination environment. The substitution of Mg 2+ and Ca 2+ ions affects the oxidation states of Ce 4+/3+ and Ru n + ions and creates oxygen vacancies, which leads to enhanced catalytic activity and reduced ethylene selectivity. A long-term stability test showed optimized catalysts Mg 0.3 La 1.7 Ce 1.8 Ru 0.2 O 7- δ and Ca 0.2 La 1.8 Ce 1.8 Ru 0.2 O 7- δ with S H 2 = 101(1)% and S H 2 = 91(2)% under OSRE conditions. The initial operation temperatures were lower than that of the unsubstituted catalyst La 2 Ce 1.8 Ru 0.2 O 7- δ . Catalysts supported on La 2 Zr 2 O 7 showed stable OSRE/ATR performance and low carbon deposition compared to catalysts supported on Al 2 O 3 . We ascribe the enhanced activity to well-dispersed alkaline earth metal and Ru ions in a solid solution structure, synergistic effects of (Mg, Ca) 2+ /Ce 3+/4+ /Ru n + ions, and a strong catalyst-support interaction that optimized the ethanol conversion and hydrogen production., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

New ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized through a solid-state reaction, and their structures were characterized using single-crystal X-ray diffraction. These compounds crystallized into a new structural type with a monoclinic space group P21/c. The structures were constructed from distorted, close-packed layers of ∞3[BaSe3]3.33– that incorporated TM atoms at octahedral sites and contained [(TM5+)2(Se2–)7(Se22–)] units. Diffuse reflectance spectra and electronic resistivity measurements indicated semiconducting properties and optical band gaps of 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra were used to investigate the interatomic interactions. Calculations of the electronic structure verified the semiconducting behavior and bonding interaction of short Se–Se contacts.

Ce(1-x)M(x)O(2) (M = Ti, Zr, and Hf) nanomaterials with controlled morphology and composition were synthesized by a two-step route for the first time. These nanomaterials exhibit high activities for hydrogen reduction and ethanol reforming reactions, and therefore, they may be useful for applications in catalysis and solid oxide fuel cells.

Quaternary selenides of Pb(4)In(x)M(6-x)Se(13) (M = Bi, x = 2.1-2.8; Sb, x = 2) were synthesized by solid-state methods, and their structures were determined from X-ray diffraction of single crystals. These compounds are isostructural with Pb(4)In(2)Bi(4)S(13) and crystallize in orthorhombic space group Pbam (No. 55) with Z = 4; the structure features a three-dimensional framework consisting of Z-shaped ribbon units and corner-sharing infinite one-dimensional [InSe(4)](infinity) chains running parallel to the c-axis, which are connected by Pb atoms to form a three-dimensional structure. Calculations of the band structure and measurements of Seebeck coefficient, electrical conductivity, and diffuse reflectance spectra confirm that these compounds are semiconductors with a narrow band gap. All compounds show semiconducting properties; the Seebeck coefficient of Pb(4)In(2.5)Bi(3.5)Se(13) is -180 microV/K at 295 K.

This work presents a detailed, combined experimental and theoretical study on the structural stability of s-p bonded compounds with the BaAl4 structure type (space group I4/mmm, Z = 2) as part of a broad program to investigate the complex questions of structure formation and atomic arrangements in polar intermetallics. From ab initio calculations employing pseudopotentials and a plane wave basis set, we extracted optimized structural parameters, binding energies, and the electronic structure of the systems AeX(III)4, AeX(II)2X(IV)2, AeX(II)2X(III)2 (Ae = Ca, Sr, Ba; X(II) = Mg, Zn; X(III) = Al, Ga; X(IV) = Si, Ge). For all systems we found a pronounced pseudo-gap in the density of states separating network X42- bonding from antibonding electronic states that coincides with the Fermi level for an electron count of 14 electrons per formula unit, the optimum value for stable BaAl4-type polar intermetallics. However, the synthesis and structural characterization (from X-ray single crystal and powder diffraction data) of the new compounds AeZn2-Al2+, AeZn2-deltaGa2+delta (Ae = Ca, Sr, Ba; delta = 0-0.2) and AeMg0.9Al3.1, AeMg1.7Ga2.3 (Ae = Sr, Ba) manifested that electron deficiency is rather frequent for BaAl4-type polar intermetallics. The site preference for different "X" elements in the ternary systems was quantified by calculating "coloring energies", which, for some systems, was strongly dependent on the size of the electropositive Ae component. The Ae2+ cations decisively influence the nearest neighbor distances in the encapsulating polyanionic networks X4(2-) and the structures of these networks are surprisingly flexible to the size of the Ae component without changing the overall bonding picture. A monoclinically distorted variant of the BaAl4 structure occurs when the cations become too small for matching the size of encapsulating X4(2-) cages. An even larger size mismatch leads to the formation of the EuIn4 structure type.

The herewith-introduced antimonides Zr(11)Sb(18) and Zr(10.4)V(0.6)Sb(18) were prepared by high-temperature techniques; both arc-melting and solid-state reactions at 1200 degrees C starting from alpha-ZrSb(2) and the metals Zr and V in powder form are possible methods. These isostructural compounds represent an unprecedented metal:antimony ratio of 11:18 and form a new structure type. Zr(11)Sb(18) crystallizes in the tetragonal space group I(-)42d, with the lattice dimensions a = 676.94(4) pm and c = 6007.3(5) pm, while the V-containing phase forms a slightly smaller unit cell with a = 676.48(8) pm and c = 6005.6(9) pm (Z = 4). Their structures are comprised of an Sb atom substructure with several intermediate Sb-Sb bonds starting at 311 pm, which is reminiscent of that found in the series (Ti,M)(5)Sb(8) (M = Zr, Hf, Nb, Mo) published last year. Interwoven with this network is the Zr atom network, which forms a diamond-like metal atom substructure with long Zr-Zr contacts of ca. 360 pm. Band structure calculations based on the linear muffin tin orbital approach reveal these antimonides to be mainly stabilized by strong M-Sb and intermediate Sb-Sb bonds, and additionally--to the smallest extent--by M-M bonds (M = Zr, V). In agreement with the electronic structure calculations, Zr(11)Sb(18) is metallic with a small positive Seebeck coefficient.

The Rh-Te and Ir-Te binary systems for 50-78 atom % Te show remarkable differences in their phase and structural features at temperatures below 1100 degrees C. Extended Hückel calculations are employed to investigate the influence of various orbital interactions on these differences. In general, a strong interrelationship among valence electron count, orbital characteristics at and near the Fermi levels, and relative strengths of M-Te, Te-Te, and M-M orbital interactions control the occurrence and structures of various M(x)()Te(2) compounds (0.75 /= (1)/(2)) to emphasize the occurrence of linear Rh(3) units in their structures. The pattern of vacancies in these structures follows the preference of Rh(4)(n)()(+3) oligomers over Rh(4)(n)()(+1) chains. Charge-iterative calculations of Rh atomic orbital energies in Rh(1+)(x)()Te(2) (x = 0.0, 0.5, 1.0) were carried out to analyze the electronic properties of Rh throughout the series. As x increases, Rh-Te orbital interactions become less attractive and the concentration of Rh-Rh repulsive interactions grows. Both effects control the maximum value of x (observed to be 0.84) for this series and influence the pattern of occupied octahedral holes in the close-packed tellurium matrix.