Synthesis and structure determination of ETS-4 single crystals

We report the hydrothermal synthesis of 10 mum x 100 mum x 10,um single cry stals of the microporous titanosilicate sodium-ETS-4. The crystallization o f large needle-shaped Na-ETS-4 crystals is preceded by the formation and su bsequent dissolution of the titanosilicate GTS-1. Large Na-ETS-4 crystals a re obtained with purity higher than 97%. The structures of Na-ETS-4 and its Sr ion-exchanged form are solved from single-crystal X-ray diffraction dat a. It is suggested from the structure solution and further supported by the results of the empirical bond valence model that the bridging unit of ETS- 4 contains five-coordinate titanium(IV). Infrared spectroscopy is also used to support the crystallographic results, with regard to the presence of ch arge-balancing protons and five-coordinate titanium. ETS-4 is, thus, one of only two synthetic titanosilicate materials containing five-coordinate tit anium. We also discuss some structural differences between ETS-4 and its na tural analogue, zorite.