| Autor: |
Friedel, P., Tobisch, J., Jehnichen, D., Bergmann, J., Taut, T., Rillich, M., Kunert, C., Böhme, F. |
| Zdroj: |
Journal of Applied Crystallography; December 1998, Vol. 31 Issue: 6 p874-880, 7p |
| Abstrakt: |
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 initiocalculations, 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. |
| Databáze: |
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