Description:
<jats:p>The quaternary systems Ba(OH)<jats:sub>2</jats:sub>—BaCl<jats:sub>2</jats:sub>—H<jats:sub>2</jats:sub>O and Ba(OH)<jats:sub>2</jats:sub>—BaBr<jats:sub>2</jats:sub>—H<jats:sub>2</jats:sub>O were studied with the help of X-ray and neutron diffraction as well as IR, Raman, DTA, and TG methods. The following compounds have been established or confirmed: Ba(OH)Cl · nH<jats:sub>2</jats:sub>O (n = 0, 1/2, 2) and Ba(OH)Br · H<jats:sub>2</jats:sub>O (n = 0, 1/2, 2). The crystal structures (of hitherto unknown structure type) of Ba(OH)Cl- 2 H<jats:sub>2</jats:sub>O and Ba(OD)Cl · 2 D<jats:sub>2</jats:sub>O were determined by single crystal X-ray methods and neutron powder diffraction (space group P4/nmm, Z = 2, 621 unique reflections, R = 8.8 and 1.9%, respectively). Whereas the hydroxide ion in this layer structured compound is non-hydrogen bonded, i. e. no Η-bond donor group, nor it is bound to the Ba<jats:sup>2+</jats:sup> ions, the water molecules are involved in strong Η-bonds to adjacent OH<jats:sup>-</jats:sup> ions. The coordination of the barium ions is monocapped tetragonal antiprismatic (4 H<jats:sub>2</jats:sub>O and 5 halide ions). The IR and Raman spectra of Ba(OH)X · 2 H<jats:sub>2</jats:sub>O (X = Cl, Br) are assigned and discussed in terms of hydrogen bonding, isotopic shifts, and intermolecular coupling of the bands observed. The stretching modes of the OH<jats:sup>-</jats:sup> ions (3672 and 3667 cm<jats:sup>-1</jats:sup>, 95 K) are shifted to higher wavenumbers by about 100 cm<jats:sup>-1</jats:sup> as compared with those of free OH<jats:sup>-</jats:sup> ions.</jats:p>