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[VIVO(O3P(CH2)2CO2)]·2H2O, 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 P21, no. 4) with cell parameters at 293 K: a = 6.4041(3), b = 17.6252(8), c = 7.7271(3) Å, β = 95.586(2)°, Z = 4, V = 868.04(7) Å3. Its framework is constituted of double chains based on isolated VIVO6 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.