Reorientational motion of hydroxide ions in solid RbOH and CsOH

Bestimmung der Strukturen von Ba(OH)Cl, Ba(OD)Cl und Ba(OD)Br durch Röntgeneinkristall- und Neutronenpulver-Messungen

The crystal structures of Ba(OD)Cl and Ba(OD)Br have been determined by neutron powder diffraction at 295 K and 1.5 K and Rietveld refinement methods {R I = 9.3, 8.2 [Ba(OD)Cl], 5.7, and 4.9% [Ba(OD)Br]}, that of Ba(OH)Cl by single-crystal X-ray diffraction at 295 K (R = 4.1% for 1260 reflections). They are isostructural to laurionite Pb(OH)Cl {space group Pnma, Z = 4, a = 738.97(3), b = 443.69(3), and c = 913.90(5) pm [Ba(OH)Cl], a = 738.07(4), b = 447.62(2) and c = 897.93(5) pm [Ba(OD)Cl] and a = 759.65(2), b = 438.77(1), and c = 1030.22(2) pm [Ba(OD)Br] at 295 K}. Whereas hydrogen bonds are not present in the bromide, in the case of Ba(OH)Cl weak hydrogen bonds to adjacent Cl− ions are formed which are strengthened on going down to lower temperatures due to reorientation of the OH− ions from trifurcated H-bonds to nearly linear ones. The hydrogen bonds of Ba(OD)Cl have been established to be stronger than those of Ba(OH)Cl. This becomes apparent by both the smaller cell volume [296.65(4) pm3 instead of 299.6(1) pm3] and the different transition temperature (170 K–300 K instead of 100 K–180 K).

Diffuse reflection infrared Fourier transform (DRIFT) spectra and high-temperature DRIFT spectra of beta-Ni(IO3)2.4H2O, Ni(IO3)2.2H2O, Mg(OH)2, and Zn(OH)F: novel embedding materials

Diffuse reflection infrared Fourier transform (DRIFT) spectra of the hydroxides Mg(OH)2 and Zn(OH)F and the iodate hydrates beta-Ni(IO3)2.4H2O and Ni(IO3)2.2H2O have been recorded at ambient and high temperature. Spectra without shifts of the band maxima compared to those of conventional infrared transmission spectra and without inversion of the bands were obtained by dilution of the compounds to about 2-10% with an appropriate embedding material. alpha-Al2O3, TiO2, ZrO2, PbF2, MgO, BaO, ZnO, Na2SiO3, SiO2 (aerosil), and powdered copper, aluminum, and magnesium were tested as diluents for hydrates and hydroxides, especially at elevated temperatures, as alternatives for the commonly used KBr. Thus, alpha-Al2O3, PbF2, and powdered copper were established as the most favorable diluents. Using these novel embedding materials, high-temperature DRIFT spectra are obtainable at temperatures not accessible with KBr discs. Dehydration and decomposition of the iodate hydrates under study were shown by change or disappearance of the respective water bands.