SYNTHESIS AND CHARACTERIZATION OF A BORON-ALUMINUM OXOCHLORIDE

A novel microporous crystalline boron-aluminum oxochloride with a cati onic framework, designated BAC(3), has been synthesized hydrothermally in the system B2O3-Al2O3-Na2O-H2O and characterized using ICP, ion ch romatograph, X-ray diffraction (XRD), magic-angle spinning nuclear mag netic resonance spectroscopy (MAS NMR), infrared spectroscopy (IR), th ermal analysis, and adsorption measurement. Some factors, such as temp erature, pH value, and anions have important effects on the crystalliz ation. Chemical analysis shows that the as-synthesized solid has the m olar composition 0.2B(2)O(3) . 1.0 Al2O3 . 0.6HCl . 5.7H(2)O. XRD anal ysis shows that the crystal has a unique framework structure. The crys tal is indexable on an orthorhombic unit cell with a = 22.55, b = 14.4 2, and c = 8.75 Angstrom. The three-dimensional framework is built up from triangular BO3 and tetrahedral BO4 units with BO3/BO4 of 2.6, as well as octahedrally coordinated Al. XRD, IR, and DTA-TG studies demon strated that the microporous crystal is unstable to thermal treatment above 300 degrees C, with the decomposition of structural H2O and HCl confirmed by mass spectroscopy analysis. On calcination above 800 degr ees C, this microporous crystal is converted via an amorphous phase to a known crystalline Al18B4O33. The measurement of adsorption of water indicates that it possesses characteristic micropore adsorption prope rties. Ion-exchange analysis shows that the Cl- anions in BAC(3) can b e partially exchanged by Br- anions, suggesting that this novel microp orous crystal has a cationic framework. (C) 1996 Academic Press, Inc.