Hydrothermal synthesis, structure determination from powder data of a three-dimensional zirconium diphosphate with an exceptionally high thermal stability:: Zr(O3P-(CH2)-PO3) or MIL-57

Zr(O3P-(CH2)-PO3) or MIL-57 was prepared in a pure form under hydrothermal conditions (3 days, 493 K, autogenous pressure). Its structure was solved ab initio from laboratory powder X-ray diffraction data. This compound is monoclinic (space group P2(1) (no. 14)) with a = 7.589(1), b = 8.110(1), c = 5.056(1) Angstrom, beta = 103.934(1)degrees, V = 302.14(1) Angstrom(3) and Z = 2. Its three-dimensional structure is built up from zirconium(IV) octahedra linked together via diphosphonate groups. This delimits a three-dimensional network with three and seven-member-ring tunnels along the c axis. The thermal behaviour, deduced from TGA and X-ray thermodiffractometry has been investigated and reveals that MIL-57 is stable under air atmosphere up to 1023 K, which is the highest temperature reported to date for a hybrid inorganic organic solid. A brief comparison between structures of MIL-57 and ZrP2O7 is also reported.