Hydrothermal synthesis and crystal structure of barium hewettite: BaV6O16 center dot nH(2)O

摘要

Ba analogues of hewettite (CaV6O16 . 9H(2)O) were synthesized by the hydrothermal methods. The compounds exhibit two phases formulated by BaV6O16 . nH(2)O and Ba1+xV6O16 . nH(2)O (x approximate to 0.2, n approximate to 3), and the structure of BaV6O16 . nH(2)O has been determined from a single crystal study. Pt crystallizes in the orthorhombic system Pnmm with 12.162(3) Angstrom, b = 10.841(4) Angstrom, c = 17.035(4) Angstrom, and Z = 6 and the structure refinements led to R = 0.066 and R-w = 0.076 for 1480 reflections with I > 3 sigma(I). The structure is basically analogous to that of gamma-Li1+xV3O8 or CaV6O16 . 9H(2)O, consisting of V6O16 layers and interstitial hydrated Ba atoms. The V6O16 layers stack along the c axis with 8.518-Angstrom spacing which is half of the c axis; adjacent layers are mirror images of each other. Ba atoms reside in three kinds of sites with totally different oxygen coordinations.Their interlayer distributions result in another long period along the b axis which is triple the ordinary 3.6-Angstrom period of the hewettite compounds. This is the first single-crystal structural study of the synthetic hewettite compounds. (C) 1998 Academic Press. [References: 24]