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.