Zur Kenntnis der Hydroxidhalogenide des Bariums. Kristallstruktur und Schwingungsspektren von Ba[O(H,D)]X · 2 (H,D)2O (X = Cl, Br) / Barium Hydroxide Halides. Crystal Structure and Vibrational Spectra of Ba[O(H,D)]X · 2 (H,D)2O (X = Cl, Br)

Abstract

The quaternary systems Ba(OH)2—BaCl2—H2O and Ba(OH)2—BaBr2—H2O 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 · nH2O (n = 0, 1/2, 2) and Ba(OH)Br · H2O (n = 0, 1/2, 2). The crystal structures (of hitherto unknown structure type) of Ba(OH)Cl- 2 H2O and Ba(OD)Cl · 2 D2O 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 Ba2+ ions, the water molecules are involved in strong Η-bonds to adjacent OH- ions. The coordination of the barium ions is monocapped tetragonal antiprismatic (4 H2O and 5 halide ions). The IR and Raman spectra of Ba(OH)X · 2 H2O (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- ions (3672 and 3667 cm-1, 95 K) are shifted to higher wavenumbers by about 100 cm-1 as compared with those of free OH- ions.