Synthesis and characterization of a new layered barium aluminate containing six-membered rings: BaAl2O3(OH)(2) center dot H2O

A new layered barium aluminate hydrate, BaAl2O3(OH)(2).H2O, has been synthe sized from a hydrothermal system. The compound crystallizes in the orthorho mbic space group Pna2(1), with M = 291.33, a = 5.642(3) Angstrom, b = 9.887 (7) Angstrom, c = 10.449(6) Angstrom, V = 582.9(6) Angstrom (3), Z = 4, R = 0.0288, and R = 0.0744. The structure of the compound consists of aluminat e sheets stacked in an ABAB sequence. Each individual sheet contains six-me mbered rings formed by corner-sharing AlO2(OH)(2) tetrahedral units with th e terminal OH groups pointing toward the interlayer region in one direction . There are Ba2+ cations and water molecules located between the adjacent a luminate sheets. On the basis of powder X-ray diffraction, the as-synthesiz ed compound converts to the BaAl2O4 phase by thermal treatment at elevated temperatures. The phase transition has also been monitored by infrared spec troscopy. (C) 2001 Academic Press.