SYNTHESIS, CRYSTAL-STRUCTURES, AND ION-EXCHANGE PROPERTIES OF A NOVEL POROUS TITANOSILICATE

A sodium titanosilicate of ideal composition Na2Ti2O3SiO4.2H2O was synthesized hydrothermally in highly alkaline media. Its crystal structure was solved from X-ray powder data by ab initio methods. The compound is tetragonal, a = 7.8082(2), c = 11.9735(4) angstrom, space group P4(2)/mcm, Z = 4. The titanium atoms occur in clusters of four grouped about the 4(2) axis and are octahedrally coordinated by oxygen atoms. The silicate groups serve to link the titanium clusters into groups of four arranged in a square of about 7.8 angstrom in length. These squares are linked to similar ones in the c direction by sharing corners to form a framework which encloses a tunnel. Half the Na+ ions are situated in the framework coordinated by silicate oxygen atoms and water molecules. The remaining sodiums are present in the cavity, but evidence indicates that some of them are replaced by protons. The composition is then closer to Na1.64H0.36Ti2O3SiO4.1.8H2O. The sodium ions within the tunnels are exchangeable. Exhaustive exchange with CsNO3 yielded a Cs+ phase of composition Na1.49Cs0.2H0.31Ti2O3SiO4.H2O whose structure was revealed from application of Rietveld methods to X-ray powder data.