Synthesis, crystal structure of the ammonium vanadyl oxalatophosphite and its controlled conversion into catalytic vanadyl phosphates

An ammonium vanadyl oxalatophosphite has been synthesized by hydrothermal treatment. The formula is (NH4)2(VOHPO3)2C2O4 2·9H2O (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(HPO3)2C2O4]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 (NH4)2(VOHPO3)2C2O4 2·9H2O thermal decomposition. The new vanadyl oxalatophosphite, (NH4)2(VOHPO3)2C2O4 2·9H2O has been prepared hydrothermally and its structure solved by combining single-crystal X-ray diffraction and Solid State NMR. Thermogravimetric studies and variable temperature X-ray diffraction showed the reversible departure of water molecules upon heating. At higher temperature, an adequate redox balance during the thermal decomposition of the material, allows to control the preparation of different catalytically active phases in the vanadyl phosphate system: ω-VOPO4 and (VO)2(P2O7). [Display omitted] •The first ammonium vanadium oxalatophosphite has been synthesized hydrothermally.•The structure has been established by combining X-ray diffraction-Solid State NMR.•The layered structure is related to that of vanadium oxalato-phosphates.•Chosen catalytic VPO phases can be prepared using adequate redox balance upon heating.