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.