SYNTHESIS, THERMAL-STABILITY, AND STRUCTURE OF (V13MO87)O2935 - A NEW OXIDE WITH THE OPEN HEXAGONAL MOO3 STRUCTURE

New oxides with the stoichiometry {LixH.13-x}(V.13Mo.87)O3 · 0.26H2O and the structure of “hexagonal MoO3” have been precipitated directly from Li-V-Mo aqueous solutions. At room temperature in dilute HCl, these precipitates undergo a rapid ion-exchange reaction to give the pure protonic form of vanadium-stabilized hexagonal MoO3, H.13(V.13Mo.87)O3 · 0.26H2O. Complete dehydration of this solid acid yields a new oxide (V.13Mo.87)O2.935 which retains the structure of hexagonal MoO3 up to 460°C. Whereas all the previously reported compounds with the hexagonal MoO3 framework have contained large stabilizing cations in the one dimensional channels of the structure, (V.13Mo.87)O2.935 represents the open form of hexagonal MoO3 and has empty channels with free diameters approaching 3.3 Å. Powder neutron diffraction was used to confirm the structure of (V.13Mo.87)O2.935 which was refined in space group P63 with final lattice parameters of a = 10.593(1), c = 3.6944(4) Å; V = 359.01 Å3. The “porosity” of this structure is significantly, ≈ 12-18%, greater than the α, β, and β′ polymorphs of MoO3. © 1993 Academic Press, Inc.