Lithium vanadyl oxalatophosphite: Influence of the water content on the crystal structures and the dehydration scheme

• The first lithium vanadium oxalatophosphite have been synthesized hydrothermally.
• The structure of these compounds is related to vanadium oxalato-phosphates.
• Hydrogen bonding in starting material influences the intermediate phase structures.
• Thermal decomposition evidences two Li2[(VO)2(HPO3)2C2O4] anhydrous polymorphs.

Two new lithium vanadyl oxalatophosphites have been synthesized by hydrothermal treatment. The respective formula are Li2(VOHPO3)2C2O4 6H2O (1) and Li2(VOHPO3)2C2O4 4H2O (2). The structures of the compounds have been determined by single crystal X-ray diffraction. Compound 1 crystallizes in triclinic symmetry in space group P-1, a=6.3592(2) Å, b=8.0789(3) Å, c=9.1692(3) Å, α=64.390(2), β=87.277(2)°, γ=67.624(2) and, compound 2 in monoclinic symmetry, space group P21/a, a=6.3555(2) Å b=12.6368(7) Å c=9.0242(4) Å β=105.167(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 lithium ions and the water molecules are located between the anionic [(VO)2(HPO3)2C2O4]2− layers. Thermal behavior of both compounds was carefully studied by combining thermogravimetric analyses and thermal dependant X-ray diffraction in order to study the thermal stability of the layered oxalatophosphites and to see the influence of the decomposition of the carbon-based anions into the final lithium vanadyl phosphate. Various intermediate phases were evidenced and for both compounds the final product was LiVOPO4.

Two new lithium vanadyl oxalatophosphites layered compounds, Li2 (VOHPO3)2C2O4 6H2O (1) and Li2 (VOHPO3)2C2O4 4H2O (2) have been hydrothermally synthesized. Lithium ions and water molecules are located between the anionic [(VO)2(HPO3)2C2O4]2− layers. Thermal behaviors were carefully studied by thermogravimetric and thermal dependant X-ray diffraction. Various intermediate phases were evidenced and for both compounds the final product was LiVOPO4.Figure optionsDownload as PowerPoint slide