STRUCTURE OF THE MICROPOROUS TITANOSILICATE ETS-10

INORGANIC microporous framework solids such as zeolites are of conside rable technological importance as shape-selective catalysts, ion-excha nge materials and molecular sieves1. Most microporous materials known until recently were silicates, aluminosilicates1 or aluminophosphates2 -4, all of which contain tetrahedrally coordinated metal atoms. In 198 9, a family of microporous titanosilicates (generically denoted ETS) w as discovered in which the metal atoms (Ti4+) are octahedrally coordin ated5-8. A full understanding of the potential of any microporous soli d to act as a molecular sieve and selective catalyst, and of the natur e of the catalytic centres, requires that its structure be known. But that of the ETS materials has proved elusive because of the considerab le degree of disorder that they contain. Using a combination of high-r esolution electron microscopy, electron and powder X-ray diffraction, solid-state NMR, molecular modelling and chemical analysis, we have no w been able to solve the structure of a prominent member of this famil y, ETS-10. This structure comprises corner-sharing SiO4 tetrahedra and TiO6 octahedra linked through bridging oxygen atoms. The pore system contains 12-membered rings and displays a considerable degree of disor der. Many ordered variants of ETS-10 exist, some of which are chiral.