The new vanadyl phosphate Na 4 VO(PO 4 ) 2 was synthesized and investigated by X-ray powder and single-crystal diffraction, high-temperature X-ray diffraction, electron diffraction, high-resolution electron microscopy, thermal analysis, magnetic susceptibility, and conductivity measurements. The compound undergoes a reversible phase transition at about 200 °C. The crystal structure of low-temperature β-Na 4 VO(PO 4 ) 2 was solved using X-ray singlecrystal data. This phase has an orthorhombic unit cell with lattice parameters a ) 16.0068(12) Å, b ) 14.5129(8) Å, c ) 7.0231(5) Å, S.G. Pbca, and Z ) 8. The crystal structure of β-Na 4 -VO(PO 4 ) 2 is built by isolated chains formed by corner-shared V 4+ O 6 octahedra linked additionally via corners by two PO 4 tetrahedra. All chains in the structure are equivalent. Na cations are located between the chains in an ordered manner. High-temperature R-Na 4 -VO(PO 4 ) 2 also has an orthorhombic cell with lattice parameters a ) 15.595(1) Å, b ) 14.651(2) Å, c ) 7.0262(6) Å, S.G. Ibam, and Z ) 8. Electron diffraction study revealed an existence of various structural transformations occurring in situ in the transmission electron microscope. In both R-and β-modifications, the susceptibility follows a Curie-Weiss law with a very small Curie-Weiss temperature, indicating a very weak magnetic exchange among the V 4+ ions.

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Vanadium Vanadium I 5000Crystal Structure, Polymorphism, and Properties of the New Vanadyl Phosphate Na 4 VO(PO 4 ) 2 . -Green single-phase powder of the title compound is prepared by solid state reaction of an equimolar mixture of Na4P2O7 and VO2 (700°C, 3 d). As revealed by powder and single crystal XRD, the compound undergoes a reversible phase transition at about 200°C. The low temperature form crystallizes in the orthorhombic space group Pbca with Z = 8. The structure contains isolated chains formed by corner-shared V IV O 6 octahedra additionally linked by two PO 4 tetrahedra. The high temperature form crystallizes in the orthorhombic space group Ibam with Z = 8. In both modifications, the susceptibility follows a Curie-Weiss law with a very small Curie-Weiss temperature, indicating a very weak magnetic exchange among the V 4+ ions. -(PANIN, R. V.; SHPANCHENKO*, R. V.; MIRONOV, A. V.; VELIKODNY, Y. A.; ANTIPOV, E. V.; HADERMANN, J.; TARNOPOLSKY, V. A.; YAROSLAVTSEV, A. B.; KAUL, E. E.; GEIBEL, C.; Chem.