S. Peter, H. Lutz, W. Jauch
1999
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Journal
Zeitschrift Fur Kristallographie
Abstract
The crystal structure of barium hydroxide iodide tetrahydrate Ba(OH)I.4 H 2 O (space group P1, No. 2, Z = 2, a = 628.1(1) pm, b = 806.1(2) pm, c = 811.8(1) pm, α = 90.47(1)°, β = 106.87(1)°, and γ = 90.97(1)°, final R1 = 0.0398 (I > 2σ(I) for 780 unique reflections) was redetermined by single-crystal neutron diffraction studies. Each of the four crystallographically different H 2 O molecules serves as donor of a very weak hydrogen bond to adjacent I - ions and quite a strong one to an OH - ion or another H 2 O molecule (H 2 O II). Hence, the hydrate H 2 O molecules are extremely asymmetrically bound. The difference of the two internal O-H distances of the H 2 O molecules Δr O-H reaches 8.1 pm at the most. As a consequence, the stretching modes of the H 2 O molecules are fully decoupled. The OH - ion donates a very weak O-H - ...I hydrogen bond and accepts three HO-H...OH - bonds. The different strength of the hydrogen bonds is discussed with respect to the acceptor capability of the hydrogen-bond acceptor groups and the various OH frequency versus r O-H and r H...Y hydrogen-bond distance correlation curves reported in the literature.