ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
A new heterocyclic compound, cyclo-tris(2,6-pyridylformamidine), was synthesized as a highly crystalline powder-like substance from which very small whiskers were produced by a sublimation technique. By rotating-crystal and powder diffraction measurements, a set of structural data were obtained which were fitted mathematically to a structural model. The fitting procedure included geometry optimization by ab initio calculations, crystal structure and X-ray diffraction pattern simulation as well as structure refinement based on the newly developed Rietveld algorithm BGMN® under force-field constraints. A single-crystal structure refinement could not be carried out because of the small size of the whiskers. In order to obtain the atomic coordinates a new procedure incorporating a powder diffraction pattern refinement was used. Cyclo-tris(2,6-pyridylformamidine) crystallizes in a monoclinic unit cell with a = 28.18 (1), b = 14.67 (1), c = 4.428 (1) Å, β = 90.10 (2)°. The symmetry was determined as P21/a. The expected threefold symmetry of the cyclic compound was disturbed in the crystallized state, in agreement with solid-state NMR investigations. The best approximation was obtained when water molecules were additionally packed into the unit cell.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889898007560
