Hybrid open frameworks:: synthesis, structure and thermal behaviour of MIL-26, a new three-dimensional vanadium(IV) ethylcarboxyphosphonate Na[VIVO(O3P(CH2)2CO2)]•2H2O

Na[(VO)-O-IV(O3P(CH2)(2)CO2)]. 2H(2)O, MIL-26, was synthesized hydrothermally at 453 K for 24 h under autogenous pressure. Its three-dimensional open structure was determined by single crystal X-ray diffraction. MIL-26 is monoclinic (space group P2(1), no. 4) with cell parameters at 293 K: a = 6.4041(3), b = 17.6252(8), c = 7.7271(3) Angstrom, beta = 95.586(2)degrees, Z = 4, V = 868.04(7) Angstrom(3). Its framework is constituted of double chains based on isolated (VO6)-O-IV octahedra linked by PO3C tetrahedral groups of the [O3PCH2CH2CO2](3-) organic cations. At the other end of each organic chain, CO2- chelates a VO6 octahedron of a neighbouring chain. Each double chain is connected to four others by these organic chains thus defining elliptical channels along [100] in which water molecules and Na+ cations are located.