The crystal structure of isopropyl 1-thio-beta-D-galactopyranoside monohydrate at 123 K.

The crystal structure of isopropyl 1-thio-beta-D-galactopyranoside monohydrate is orthorhombic, P2(1)2(1)2(1), Z = 4, with cell dimensions at 123 K [293 K] of a = 7.983(1) [8.037(1)], b = 24.574(5) [24.709(4)], c = 6.329(1) [6.3736(8)] A, V = 1241.84 [1265.71] A3. The calculated and measured density is Dx = 1.371 [1.345] g cm-3, Dm = [1.340] g cm-3. Diffraction data were obtained with CuK alpha radiation and a Nonius CAD-4 diffractometer. The structure was solved by using MULTAN, and refined to R(F2) = 0.051, RW(F2) = 0.078, R(F) = 0.029, S = 1.16 for 1502 reflections. The molecule has the 4C1(D) conformation. The orientation of the primary alcohol group is gauche/trans, and that about the glycosidic C-S bond is (-)synclinal relative to the ring C-O bond. Although this compound does not form thermotropic liquid crystals, it has two crystal-to-crystal phase-transitions, at 70 and 104 degrees, prior to melting at 126 degrees. The crystal structure has a characteristic, amphiphilic, head-to-head bilayer molecular packing, with intercalated alkyl groups. The water molecule is included in the hydrogen-bond structure that links the galactoside moieties.