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

Abstract

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 P2₁ (no. 14)) with a = 7.589(1), b = 8.110(1), c = 5.056(1) Å, β = 103.934(1)°, V = 302.14(1) ų 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.