Abstract

The ZnCl₂–H₂O₃P-CH₂-PO₃H₂–NaOH–H₂O quaternary system was investigated under hydrothermal conditions as a function of pH (48 h; 443 K). Zn₂(H₂O){O₃P-CH₂-PO₃} (labelled VSB-3(Zn)) and NaZn₂(OH){O₃P-CH₂-PO₃}·1.5H₂O (labelled MIL-48) are obtained at pH 1 and 9 respectively. Their structures were solved from single crystal X-ray diffraction. Zn₂(H₂O){O₃P-CH₂-PO₃}, isostructural with Co and Ni analogues previously described, is monoclinic (C 2/c (n° 15)) with lattice parameters a = 18.7573(3) Å, b = 8.2803(2) Å, c = 8.9225(1) Å, β = 106.815(1)°, V = 1326.56(4) ų, Z = 8, R1(F_o) = 0.0269 and wR2(F_o²) = 0.0704 for 1735 unique reflections I ≥ 2σ(I). Its thermal evolution first leads to anhydrous Zn₂{O₃P-CH₂-PO₃} (labelled VSB-4(Zn)) whose structure was refined from XRD powder pattern, then to γ and β zinc diphosphates successively. NaZn₂(OH){O₃P-CH₂-PO₃}·1.5H₂O is monoclinic (P2₁/c (n° 14)) with lattice parameters a = 8.9929(9) Å, b = 5.5093(6) Å, c = 18.025(2) Å, β = 92.376(2)°, V = 892.3(2) ų, Z = 4, R1(F_o) = 0.0700 and wR2(F_o²) = 0.1078 for 2358 unique reflections I ≥ 2σ(I). Its three-dimensional structure provides a new zeotype with 10-membered channels where the Na⁺ cations and the water molecules are encapsulated. The elimination of water provides a new compound, NaZn₂(OH){O₃P-CH₂-PO₃} (labelled MIL-48_calc), whose structure was refined from XRD powder pattern.