Showing papers in "Acta Crystallographica in 1986"

Charge density in Cuprite, Cu2O

Abstract: Etude de l'influence des procedures de reduction de donnees, des modeles de facteur de temperature et des modeles de deformation sur les resultats

Three Crystalline Forms of 9-(2-Hydroxyethyl)adenine Resulting from the Different Stacking of Hydrogen-Bonded Layers.

Abstract: Three crystalline forms of the title compound [CTH9N50 , M r = 179.2, 2(Cu Ktx) = 1.54184 .A, room temperature] were examined by X-ray diffraction. Form (I): orthorhombic, P212~2 l, a = 13-566(2), b = 8 . 2 7 1 ( 1 ) , c = 7 . 3 4 0 ( I ) A , V = 8 2 3 . 6 ( 2 ) A 3, Z = 4, D x = 1.445 gcm -3, F(000) = 376, ~ = 8.88 cm -1, R = 0.070, 701 observed reflexions. Form (II): orthorhombic, P2~2121, a 1 3 . 5 7 2 (3), b = 8 . 2 4 8 ( 2 ) , c = 14.508 (3)/k, V-1624.1 (6)/k 3, Z = 8, D m = 1.466, D x = 1.466 g cm -3, F(000) = 752, /t = 9.01 cm -l, R -0.047, 1478 observed reflexions. Form (III): monoclinic, P21/e, a = 13.543 (1), b = 8.290 (1), c = 22.591 (2) A, f l= 104.97 (1) °, V = 2450.2 (4) A 3, Z = 12, Dx= 1.457 g cm -3, F(000) = 1128, ~t = 8.96 cm -1, R = 0.105, 2339 observed reflexions. In the three forms, the values of a and b remain nearly the same, but those of c are in the ratio of 1:2:3. In all three structures, adenine moieties are connected by N(6)H.. .N(1) and N(6)H.. .N(7) hydrogen bonds to form infinite ribbons along b, and the ribbons are linked side by side via O(12)H.. .N(3) to construct hydrogenbonded pleated sheets. The sheet in form (I) consists of one crystallographic kind of molecule, A, while that in form (II) contains two kinds of molecules, B and C. Form (III) has two kinds of sheet: one consists of D and the other of E and F molecules. There are no significant differences in molecular dimensions among the molecules A-F, and the four kinds of sheets are almost the same. However, three different stacking modes exist between successive layers. Different combinations of the stacking modes result in poly0108-2701/86/101336-05501.50 morphism. Disorder along ¢* observed in forms (I) and (III) and twinning in form (Ill) are interpreted in terms of the stacking modes. Introduction. Polymorphism, twinning and disorder owing to layer stacking can give much information for intermolecular interactions of complicated molecules. However, detailed reports on these crystallographic aspects for organic substances are not common, one example being that of o-chlorobenzamide (Kato, Takaki & Sakurai, 1974). The present compound, which was synthesized as a model of protein-nucleic acid interactions, gives rise to three crystalline forms; the values of one of the lattice parameters are in the approximate ratio 1:2:3, while the other two do not change significantly. Forms (I) and (III) reveal features of disorder about this multiplicable lattice vector, dependent on the crystallization conditions, and form (III) is also constituted of finely polysynthetic twins. The present paper describes the varieties of stacking of the typical hydrogen-bonded molecular layers, found in the structures of the three

Room Temperature Phase of n-Decylammonium Chloride

Abstract: Cristallisation dans le systeme monoclinique, groupe P2 1 et affinement jusqu'a R=0,032. Le caractere amphiphile de l'ion provoque la cristallisation en couches