A first example of polyoxotungstate-based giant molecule. Synthesis and molecular structure of a tetrapod-shaped Ti-O-Ti bridged anhydride form of Dawson tri-titanium(IV)-substituted polyoxotungstate

The preparation and structural characterization of a giant "tetrapod"-shaped inorganic molecule, [((alpha)-1,2,3-P2W15Ti3O60.5)4Cl] 37- ,1a(abbreviated to {TiO6}12; FW ~15700), consisting of four tri-TiIV-1,2,3-substituted -Dawson substructures and one encapsulated Cl- ion, are described. A water-soluble, all-inorganic composition compound of the tetrameric Ti-O-Ti bridged anhydride form, NaxH33-xK4[1a].yH2O, 1(x= 21-26, y= 60-70), being afforded by a stoichiometric reaction in aqueous solution of tri-lacunary Dawson polyoxotungstate Na12[B-(alpha)-P2W15O56].19H2O with 3 equiv of Ti(SO4)2.4H2O in HCl-acidic aqueous solution followed by exchanging the countercation, was obtained as analytically pure, homogeneous colorless plate crystals. Single-crystal X-ray structure analysis revealed that the polyoxoanion 1a was an inorganic, giant "tetrapod"-shaped molecule (described as a sphere with a diameter of ~31.2 (angstrom)) with approximately Td symmetry. Characterization of 1 was also accomplished by complete elemental analysis, TG/DTA, FTIR, UV-vis absorption and solution (31P and 183W) NMR spectroscopy.