Neutron Powder Diffraction Study of Ti2(OH)2OSiO4·1.5H2O
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The proton form of the exchanger Na2Ti2O3(SiO4)·2H 2O exhibits a high selectivity for Cs+ even in acid solutions. A neutron diffraction study was carried out to locate the position of the exchangeable protons. The structure contains cubane-like Ti4O4 clusters bridged by silicate groups. The acidic proton is located on the cubane oxygens which make them four-coordinate, being bonded to three titaniums and one proton. The unit cell is tetragonal, a = 11.0343(5) Å, c = 11.8797(7) Å, space group P42/mbc, Z=8. There are six water molecules per tunnel and two tunnels per unit cell. Thus, the empirical formula is Ti2(OH)2OSiO4·1.5H2O. The water molecules are H-bonded to the framework oxygens and to each other. Although the tunnels are filled with water molecules, framework sites normally occupied by Na+ are empty. The high selectivity for Cs+ apparently stems from the ability to form a thermodynamically stable eight-coordinate complex by replacement of the hydroxyl protons. © 1999 American Chemical Society.
author list (cited authors)
Pertierra, P., Salvado, M. A., Garcia-Granda, S., Bortun, A. I., & Clearfield, A.