Crystal structure of (−)- Δ16(17)-dehydrolupaninium perchlorate from sealed-tube and synchrotron X-ray diffraction data

Abstract

Two independent X-ray structure determinations on the same crystal sample of the lupine alkaloid (−)- Δ 16(17)-dehydrolupaninium perchlorate, [C 15H 23N 2O] +·ClO − 4, were carried out, one using a laboratory 4-circle diffractometer equipped with a sealed X-ray tube, and the other, a 6-circle diffractometer installed at the Swiss-Norwegian beam line at the ESRF in Grenoble. The same crystal sample was used but different setting angles for positioning reflections were applied. The measurements provide the most precise dimensions obtained so far for the immonium group. Both determinations reveal consistent details of the dehydrolupaninium cation structure and of ClO − 4 anion distortions. The cation rings A, B, C and D assume distorted half-chair, chair, distorted sofa, and chair conformations, respectively. No short electrostatic interactions between the immonium group and the perchlorate anion are observed, in contrast to all previous studies.