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An ammonium vanadyl oxalatophosphite has been synthesized by hydrothermal treatment. The formula is (NH 4 ) 2 (VOHPO 3 ) 2 C 2 O 4 2·9H 2 O (1) . The crystal structure of the compound has been determined by single crystal X-ray diffraction and solid state Nuclear Magnetic Resonance spectroscopy (NMR). Compound 1 crystallizes in triclinic symmetry with space group P −1, a = 6.3844(4) Å, b = 7.2278(4) Å, c = 9.2965(5) Å, α = 67.260(4)°, β = 72.927(4)°, γ = 85.848(3)°. The vanadium phosphite framework consists of infinite chains of corner-sharing vanadium octahedra and hydrogenophosphite tetrahedra. The oxalate groups ensure the connection between the chains. The ammonium ions and the water molecules are located between the anionic [(VO) 2 (HPO 3 ) 2 C 2 O 4 ] 2 − layers. The thermal behaviour of 1 was carefully studied by combining thermogravimetric analyses, in situ X-ray diffraction and Infrared spectroscopy. The formation of given vanadyl phosphate catalysts was shown to be atmosphere-dependent of (NH 4 ) 2 (VOHPO 3 ) 2 C 2 O 4 2·9H 2 O thermal decomposition. [ABSTRACT FROM AUTHOR]

The vanadyl oxalatophosphate Na2[(VO)2(HPO4)2C2O4]·2H2O has been synthesized by hydrothermal treatment. Its structure has been determined and refined by combining X-ray powder diffraction and solid-state NMR techniques. It crystallizes with monoclinic symmetry in space group P21, a = 6.3534(1) Å, b = 17.1614(3) Å, c = 6.5632(1) Å, β = 106.597(1)°. The structure is related to that of (NH4)2[(VO)2(HPO4)2C2O4]·5H2O, which was previously reported. The vanadium phosphate framework consists of infinite [(VO)(HPO4)] chains of corner-sharing vanadium octahedra and hydrogenophosphate tetrahedra. The oxalate groups ensure the connection between the chains to form a 2D structure. The sodium ions and the water molecules are located between the anionic [(VO)2(HPO4)2C2O42 layers. The thermal decomposition has been studied in situ by temperature-dependent X-ray diffraction and thermogravimetry. It takes place in three stages, where the first two correspond to water removal and the last to the decomposition of the oxalate group and water elimination, leading to the final product NaVOPO4. [ABSTRACT FROM AUTHOR]

We carried out a detailed investigation of the local ordering and dynamics of the lithium intercalation in paramagnetic Li x VOPO 4.2H 2 O (with 0 < x ≤ 1) materials. This question was addressed using a combination of X-ray diffraction, 31P and 7Li MAS NMR experiments. We first studied the structure of the fully ordered end-member of the series, Li 1 VOPO 4.2H 2 O, revisiting the X-ray single crystal diffraction data on the basis of the information provided by 31P MAS NMR. We then carried out 7Li MAS and exchange NMR experiments and 31P MAS experiments on the polycrystalline powders obtained after partial lithium insertion in VOPO 4.2H 2 O phases. These experiments evidenced an unexpected ageing of the material related with lithium dynamics between the VOPO 4 layers and a V4+/V5+ charge ordering mechanism within the layers. Image 1 • Combination of single crystal X-Ray diffraction and 31P MAS NMR allowed us to revisit the symmetry of Li 1 VOPO 4.2H 2 O. • 7Li EXSY NMR combined to XRD on Li 0.5 VOPO 4.2H 2 O evidenced an ordering mechanism of Li cations (timescale of several days). • 31P NMR are showing a similar rearrangement taking place within the layers with an ordering of the V4+ versus V5+ locations. [ABSTRACT FROM AUTHOR]