Local pseudosymmetry of the water molecule in BaBr₂ · 2H₂O, a neutron diffraction study

Abstract

Barium bromide dihydrate, BaBr 2 · 2H 2 0, M r = 333.188, monoclinic C2/c, a = 1042.9(1), è = 719.5(1), c = 837.5(1) pm, β = 113.60(1)°, V= 0.5759(1) nm 3 , Ζ = 4, D x = 3.843 Mg · m" 3 ,/l(neutron) = 123.75 pm, /i(calc.) = 0.146 mm" 1 , F\000) = 61.746 fm, Γ =297 Κ, R = 0.0494, wR = 0.0469 for 370 observed unique reflections. The present neutron diffraction study confirms the results of X-ray structure determination with respect to the heavy atoms. Additionally, previous spectroscopic findings can now be related to structural features. The energetic equivalence of the two crystallographically independent OH bonds can be explained by (i) the very similar hydrogen bond lengths [Η···ΒΓ: 243.7(6) and 244.3(7) pm] and (ii) the symmetric coordination sphere of the tetrahedrally coordinated water molecules. The occurence of almost tetrahedral * Author to whom correspondence should be addressed. Brought to you by | provisional account Unauthenticated Download Date | 6/22/15 8:05 AM 176 Th. Kellersohn et al.[Br 2 (H 2 0) 2 ] 2 ~ units enables significant intermolecular vibrational interactions of the water molecules, which explains the unusually large Davydov splittings of the water bands.

Solid-State 79/81Br NMR and Gauge-Including Projector-Augmented Wave Study of Structure, Symmetry, and Hydration State in Alkaline Earth Metal Bromides

“…Single-crystal XRD , and neutron diffraction studies confirm that BaBr 2 ·2H 2 O belongs to the monoclinic C 2/ c space group. The bromine atoms are at 1 lattice positions, which place no symmetry restrictions on the QI and CSA tensor parameters.…”

Solid-State 127I NMR and GIPAW DFT Study of Metal Iodides and Their Hydrates: Structure, Symmetry, and Higher-Order Quadrupole-Induced Effects

“…For the I, O, and H atoms, the initial guess was set to the analogous atomic positions in SrCl 2 ·6H 2 O. For BaI 2 ·2H 2 O, no structural data exist but based upon prior 127 I NQR data , it is suspected to be isostructural to BaBr 2 ·2H 2 O, the structure of which is known . Hence, the BaBr 2 ·2H 2 O crystal structure was used as the starting point when optimizing the BaI 2 ·2H 2 O crystal structure.…”