Hydrothermal Synthesis and Crystal Structure of Barium Hewettite: BaV6O16·nH2O

✍ Scribed by Yoshio Oka; Takeshi Yao; Shoichi Sato; Naoichi Yamamoto

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 637 KB
• Volume: 140
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7879

✦ Synopsis

Ba analogues of hewettite (CaV 6 O 16 • 9H 2 O) were synthesized by the hydrothermal methods. The compounds exhibit two phases formulated by BaV 6 O 16 • nH 2 O and Ba 1؉x V 6 O 16 • nH 2 O (x+0.2, n+3), and the structure of BaV 6 O 16 • nH 2 O has been determined from a single crystal study. It crystallizes in the orthorhombic system Pnmm with a ‫؍‬ 12.162(3) A s , b ‫؍‬ 10.841(4) A s , c ‫؍‬ 17.035( 4) A s , and Z ‫؍‬ 6 and the structure refinements led to R ‫؍‬ 0.066 and R w ‫؍‬ 0.076 for 1480 reflections with I'3 (I). The structure is basically analogous to that of -Li 1؉x V 3 O 8 or CaV 6 O 16 • 9H 2 O, consisting of V 6 O 16 layers and interstitial hydrated Ba atoms. The V 6 O 16 layers stack along the c axis with 8.518-A s 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-A s period of the hewettite compounds. This is the first single-crystal structural study of the synthetic hewettite compounds.