B. Manoun

Vibrational Spectra and Factor Group Analysis of M0.50TiOPO4 Oxyphosphates (M = Mg, Zn, Ni, Co, Fe and Cu)

Raman spectra of a series of orthophosphates M(0.50)TiO(PO(4)) (M=Mg, Zn, Ni, Co, Fe, and Cu) have been recorded in crystalline state. Factor group analysis has been performed for space group P2(1)/c and assignments of the internal modes of the [PO(4)] tetrahedra and [TiO(6)] octahedra have been made.

High temperature and composition induced phase transitions in LiZnV1−xAsxO4 phenacites: Crystal structure and Raman spectroscopy studies

In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1-xAsxO4 (0⩽x⩽1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x=0.7 and x=0.8. Furthermore, increasing temperature for the compositions (0.8⩽x⩽1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x=0.7 and 0.8.

Pentaammonium heptasodium [bis(μ5-phosphato) pentakis (μ2-oxido)-decaoxidopentamolybdenum(VI)] henicosahydrate

The title compound, (NH4)5Na7[Mo5P2O23]2·21H2O, was prepared under atmospheric conditions in aqueous solution at room temperature. The structure contains the [Mo5P2O23]6− heteropolyoxometallate anion, which has been previously reported a number of times with a variety of differing counter-cations. Each anion is built up of five MoO6 octahedra sharing an edge and forming a ring which is closed by common corners of the terminal octahedra. The rings are closed on both sides by two asymmetric PO4 tetrahedra, sharing three corners with three MoO6 octahedra. The anions are chiral and the two independent anions in the asymmetric unit were arbitarily chosen with the same chirality, but the centrosymmetric crystal contains both enantiomers. The structure can alternatively be described as a succession of layers parallel to (101), formed by the [Mo5P2O23]6− anions and linked by sodium chains. Water molecules and ammonium ions fill the remaining space and ensure the cohesion through extensive N—H⋯O and O—H⋯O hydrogen bonding.

Penta­ammonium hepta­sodium bis­[penta­kis(μ2-oxido)deca­oxido­bis­(μ5-phosphato)penta­molybdenum(VI)] henicosa­hydrate

The title compound, (NH4)5Na7[Mo5P2O23]2·21H2O, was prepared under atmospheric conditions in aqueous solution at room temperature. The structure contains the [Mo5P2O23]6− heteropolyoxometallate anion, which has been previously reported a number of times with a variety of differing counter-cations. Each anion is built up of five MoO6 octahedra sharing an edge and forming a ring which is closed by common corners of the terminal octahedra. The rings are closed on both sides by two asymmetric PO4 tetrahedra, sharing three corners with three MoO6 octahedra. The anions are chiral and the two independent anions in the asymmetric unit were arbitarily chosen with the same chirality, but the centrosymmetric crystal contains both enantiomers. The structure can alternatively be described as a succession of layers parallel to (101), formed by the [Mo5P2O23]6− anions and linked by sodium chains. Water molecules and ammonium ions fill the remaining space and ensure the cohesion through extensive N—H⋯O and O—H⋯O hydrogen bonding.

Pentaammonium heptasodium bis[pentakis(μ2-oxido)decaoxidobis(μ5-phosphato)pentamolybdenum(VI)] henicosahydrate

The title compound, (NH4)5Na7[Mo5P2O23]2·21H2O, was prepared under atmospheric conditions in aqueous solution at room temperature. The structure contains the [Mo5P2O23]6− heteropolyoxometallate anion, which has been previously reported a number of times with a variety of differing counter-cations. Each anion is built up of five MoO6 octahedra sharing an edge and forming a ring which is closed by common corners of the terminal octahedra. The rings are closed on both sides by two asymmetric PO4 tetrahedra, sharing three corners with three MoO6 octahedra. The anions are chiral and the two independent anions in the asymmetric unit were arbitarily chosen with the same chirality, but the centrosymmetric crystal contains both enantiomers. The structure can alternatively be described as a succession of layers parallel to (101), formed by the [Mo5P2O23]6− anions and linked by sodium chains. Water molecules and ammonium ions fill the remaining space and ensure the cohesion through extensive N—H⋯O and O—H⋯O hydrogen bonding.