The infrared absorption and laser Raman spectra of BaCl2·2H2O powder and single crystals as well as BaCl2·2D2O, partially deuterated, and isotopically dilute samples have been analyzed in the range from 30 to 4000 cm−1. A revised interpretation of the observed water bands is given. The influence of the bond angle of the H2O molecules both on Raman intensity of the water modes and frequency shift of the bending fundamentals is discussed. The librational modes are assigned with regard to isotopic shifts and intensities of these modes in the ir and Raman spectra. The predicted splitting of librational fundamentals of HDO molecules, which are in an asymmetric force field, has been observed. The amount of intramolecular and intermolecular coupling of the H2O vibrations is discussed.

Low temperature infrared and raman spectra of polycrystalline BaBr2.2H20 at different degrees of deuteration are studied in the frequency range from 4000 to 30cm-'. The single peaks observed for the bending fundamentals of isotopically dilute H 2 0 and D20 show that the molecules of the water of crystallization are equivalent, as required by Bang's structure determination. The singlets observed for the three fundamentals of isotopically dilute HDO show that there is a symmetric force field in the water molecules which is not predicted from the structure determination. In BaBr2.2H20 weak hydrogen bonds to the bromine ions are present which are largely bent. From the shift of the stretching modes relative to the frequencies of free water the hydrogen bond entbalpy was found to be 20 kJ. The temperature shifts of all the stretching modes are positive, which is not in agreement with Falk's results on bent hydrogen bridges. The internal modes and the twisting libration of the water molecules show an unusual large correlation splitting due to intermolecular coupling of the vibrations of the two water molecules in the 2Br-.2H20 structure unit.Bariumbromid-Dihydrat kristallisiert in der monoklinen Raumgruppe C2/c mit vier Formeleinheiten in der Elementarzelle. '.' Die Kristallwassermolekule des BaBr2.2H20 sind kristallographisch aquivalent. Herausragende Baueinheiten sind Gruppen aus 2Br--Ionen und 2H2O-Molekiilen (vgl. Abb. 1). Die Wasserstoff atome der H20-Molekiile bilden schwache Wasserstoffbrucken zu den Br--Ionen der Baueinheit aus. Die OBr-Bindungsabstande, 325 und 331 pm, unterscheiden sich relativ stark; der BrOBr-Winkel ist mit 79,2" erheblich kleiner als der Bindungswinkel der Wassermolekule.Schwingungsspektroskopische Untersuchungen, iiber die im folgenden berichtet wird, zeigten jedoch, dal3 sich die Kristallwassermolekule (Lagesymmetrie CI) in einem Gitterpotential der Symmetrie CZv befinden. Dieser Befund und eine ungewohnlich grol3e intermolekulare Kopplung der Schwingungen der Kristallwassermolekule veranlal3ten uns, das IR-und Ramanspektrum des Bariumbromid-Dihydrats, die bisher nur sehr unvollstandig untersucht ~u r d e n ,~-~ naher zu analysieren. ERGEBNISSEDie Abzahlung der optischen Schwingungen ( k = 0) des BaBr2.2H20 zeigt Tabelle 1. Ramanaktiv slnd die Schwingungen der Rassen A , und B,, IR-aktiv die Schwingungen des Typs A , und B,. Die drei inneren Schwingungen (uasym, vsym,und 6 ) sowie die drei Librationen (& R,, R,] der Kristallwassermolekule treten in t XVIII. Mitt.: H. Haeuseler und H. D. Lutz, J. Solid State Chem.

Abstract By phase analysis in the ternary systems Li-Zn(Cd or In)-Sn(Pb) several nonvalent cubic phases were found. Structure deter-mination on Li7.72Zn4.28Sn4 showed that the phases crystallize in a modified NaTl-type-lattice.

~ ~~The infrared absorption and Raman spectra of SrClz-2H20 powder as well as SrClZ.2Dz0, and partially deuterated and isotopically dilute samples, have been recorded in the range from 30 to 4000 cm-' at 95 and 295 K and analysed with regard to the strongly asymmetric force field in the H 2 0 molecules. This is shown by an unusually large splitting of the OH and OD stretching fundamentals of the HDO molecules: 3426 and 3243 cm-' and 2534 and 2408 cm-' respectively at 95 K. Uncoupled OD stretching frequencies of SrC12.6H20 and SrCI,-HzO are also presented. In SrClz.2H20 both a relatively strong and a weak hydrogen bond to chloride ions are present; these are essentially straight. The spectra of SrCIz-2Hz0 exhibit the following characteristics: (1) no intramolecular coupling of the OH stretching vibrations; (2) very large Fermi resonance of vOH and 2 & 4 (3) the same high intensity of HzO twisting librations in the infrared spectra as for wagging and rocking modes; (4) splitting of the librational fundamentals of the HDO molecules, as large as 100 cm-', caused by different structural arrangements of the H and D atoms in the asymmetric HzO molecules; and (5) strong intermolecular coupling of bending and librational fundamentals, which results in correlation splittings up to 75 cm-'. Possibilities of assigning the librational modes of HzO molecules which are in an asymmetric force field are discussed.