D. Riou and G. Férey
The hydrothermal synthesis and structure determinations of two vanadium propylenediphosphonate compounds are presented. MIL-7, formulated as [(VO)2(OH)(H2O){O3P(CH2)3PO3}](H2O)2(NH4), is synthesized at 200°C. Its structure is monoclinic [space group C2/c (no. 15)] with lattice parameters a=14.2928(2) Å, b=10.2440(2) Å,c=18.9901(1) Å, β=96.658(1)°, V=2761.69(7) Å3, Z=8. The three-dimensional framework is built up from inorganic VIV-P-O layers strongly related by the alkyl chains. Upon heating hydrothermally the same initial mixture but at 170°C one obtains a different phase, formulated as [V2O3(H2O){O3P(CH2)3PO3}](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) Å, b=10.2903(6) Å, c=18.515(1)Å,β=101.079(1)°, V=2785.9(3) Å3, Z=8. The topology of the inorganic layers is almost identical, but presents a mixed valence VIV-VV state in a 1:1 ratio.