Abstract

Two new lithium vanadyl oxalatophosphites have been synthesized by hydrothermal treatment. The respective formula are Li-2(VOHPO3)(2)C2O4 6H(2)O (1) and Li-2(VOHPO3)(2)C2O4 4H(2)O (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) angstrom, b=8.0789(3) angstrom, c=9.1692(3) angstrom, alpha=64.390(2), beta=87.277(2)degrees, gamma=67.624(2) and, compound 2 in monoclinic symmetry, space group P2(1)/a, a=6.3555(2) angstrom b=12.6368(7) angstrom c=9.0242(4) angstrom beta=105.167(3)degrees. 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)(2)C2O4](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. (C) 2014 Elsevier Inc. All rights reserved.