Synthesis and structure of a layered titanosilicate catalyst with five-coordinate titanium

TITANIUM occurs widely in the Earth's crust, traces of it being present in most rocks, soils and flays. It is estimated that titanosilicate minerals alone number more than 100; but, remarkably, in only one of these does the Ti(IV) ion take up five-fold coordination. This is in fresnoite(1) (Ba2TiSi2O8), which contains square-pyramidal TiO5 polyhedra. In the course of a programme(2-11) to produce new microporous and mesoporous solid catalysts, we have discovered an unusual non-centrosymmetric, tetragonal layered solid (Na4Ti2Si8O22.4H(2)O), designated JDF-L1, which promises to have interesting applications in materials chemistry. This material contains five-coordinate Ti(IV) ions in the form of TiO5 square pyramids in which each of the vertices of the base is linked to SiO4 tetrahedra [TiO . O-4(SiO3)(4)] to form continuous sheets. The structure was solved by applying ab initio methods to data obtained by X-ray absorption spectroscopy and powder X-ray diffraction. The interlamellar Na+ ions of JDF-L1 are replaceable by protonated amines, and after treatment with a mixture of dilute acid and hydrogen peroxide the parent solid selectively oxidizes phenol to quinone. These results indicate that the material should have useful catalytic, intercalation and ion-exchange properties analogous to those of aluminosilicate clays.