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.