Structural and vibrational study of diarsenate barium: Ba2As2O7

A new barium diarsenate with layer structure has been synthesized by solid-state method. The single crystal structure was solved and refined by X-ray diffraction. The crystal is triclinic, space group \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P\bar 1$$\end{document}, a = 7.384(2) Å, b = 7.402(2) Å, c = 13.318(2) Å; α = 93.69(2)°, β = 96.90(2)°, γ = 90.15(2)°, Z = 4 and V = 721.05(3) Å3. Its structure is composed of BaO8/BaO9 polyhedra and As2O7 bitetrahedral units of dichromate type. These groups are linked by corner and edge-sharing forming a three-dimensional framework. Two unique diarsenate groups are repeated by lattice translations to form layers. The As2O7 groups are eclipsed within As-O-As angle of 9.726° and 13.586°. The infrared and the Raman spectra of this compound are reported and discussed.