Synthesis and Characterization of a New Layered Barium Aluminate Containing Six-Membered Rings: BaAl2O3(OH)2·H2O

A new layered barium aluminate hydrate, BaAl2O3(OH)2·H2O, has been synthesized from a hydrothermal system. The compound crystallizes in the orthorhombic space group Pna21 with M=291.33, a=5.642(3) ?, b=9.887(7) ?, c=10.449(6) A, V=582.9(6) A3, Z=4, R=0.0288, and RW=0.0744. The structure of the compound consists of aluminate sheets stacked in an ABAB sequence. Each individual sheet contains six-membered rings formed by corner-sharing AlO2(OH)2 tetrahedral units with the terminal OH groups pointing toward the interlayer region in one direction. There are Ba2+ cations and water molecules located between the adjacent aluminate sheets. On the basis of powder X-ray diffraction, the as-synthesized compound converts to the BaAl2O4 phase by thermal treatment at elevated temperatures. The phase transition has also been monitored by infrared spectroscopy.