Hybrid open frameworks (MIL-n). Part 3 - Crystal structures of the HT and LT forms of MIL-7: a new vanadium propylenediphosphonate with an open-framework. Influence of the synthesis temperature on the oxidation state of vanadium within the same struc

摘要

The hydrothermal synthesis and structure determinations of two vanadium propylenediphosphonate compounds are presented. MIL-7, formulated as [(VO)(2)(OH)(H2O) {O3P(CH2)(3)PO3}](H2O)(2)(NH4), is synthesized at 200 degrees C. Its structure is monoclinic [space group C2/c (no. 15)] with lattice parameters a = 14.2928(2) Angstrom, b = 10.2440(2) Angstrom, c = 18.9901(1) Angstrom, beta = 96.658(1)degrees, V = 2761.69(7) Angstrom(3), Z = 8. The three-dimensional framework is built up from inorganic V-IV P-O layers strongly related by the alkyl chains. Upon heating hydrothermally the same initial 1 mixture but at 170 degrees C one obtains a different phase, formulated as [V2O3(H2O){O3P(CH2)(3)PO3}](H2O)(2)(NH4), the structure of which is closely related to MIL-7. Its symmetry is monoclinic [space group C2/c (no. 15)] with lattice parameters a = 14.8998(8) Angstrom, b = 10.2903(6) Angstrom, c = 18.515(1) Angstrom, beta = 101.079(1)degrees, V = 2785.9(3) Angstrom(3), Z = 8. The topology of the inorganic layers is almost identical, but presents a mixed valence V-IV-V-V state in a 1 : 1 ratio. [References: 19]