Microporous hybrid compounds: hydrothermal synthesis and characterization of two zinciomethylenediphosphonates with 3D structures, structure determination of their dehydrated forms

摘要

The ZnCl_2-H_2O_3P-CH_2-PO_3H_2-NaOH-H_2O quaternary system was investigated under hydrothermal conditions as a function of pH (48 h; 443 K). Zn_2(H_2O){O_3P-CH_2PO_3} (labelled VSB-3(Zn)) and NaZn_2(OH) {O_3P-CH_2-PO_3}·1.5H_2O (labelled MIL-48) are obtained at pH 1 and 9 respectively. Their structures were solved from single crystal X-ray diffraction. Zn_2(H_2O){O_3P-CH_2-PO_3}, isostructural with Co and Ni analogues previously described, is monoclinic (C 2/c (n deg 15)) with lattice parameters a = 18.7575(3)A, b = 8.2803(2)A, c = 8.9225(1), A, beta = 106.815(1) deg, V = 1326.56(4) A~3, Z = 8, R1(F_o) = 0.0269 and _WR2(F_o~2) = 0.0704 for 1735 unique r4eflections I >= 2 sigma (I). Its thermal evolution first leads to anhydrous Zn_2{O_3P-CH_2PO_3} (labelled VSB-4(Zn)) whose structure was refined from XRD powder pattern, then to gamma and beta zinc diphosphates successively. NaZn_2(OH){O_3P-CH_2-PO_3}·1.5H_2O is monoclinic P2_1/c (n deg 14) with lattice parameters a = 8.9929(9) A, b = 5.5093(6) A, c = 18.025(2) A, beta = 92.376(2) deg, V = 892.3(2)A~3, Z = 4, R1(F_o) = 0.0700 and wR2(F_o~2) = 0.1078 for 2358 unique reflections I >= 2sigma (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, NaZn_2(OH) {O_3P-CH_2-PO_3} (labelled MIL-48_(calc)), whose structure was refined from XRD powder pattern.