Competition between #pi#-#pi# stacking and hydrogen bonding in (1:2) picrates of 1,5-diamino-3-oxapentane,1,8-diamino-3,6-dioxaoctane and 1,5-diamino-3-azapentane-solid state studies

摘要

Crystallographic studies of (2: 0 salts of picric acid with 1,5-diamino-3-oxapentane (I OPICR), 1,8-diamino-3,6-dioxaoctane (20PICR) arid 1,5-diamino-3-azapentane (lNPICR) showed significant conformational change of the picrate ion due to numerous electrostatic, H-bonding and 7r-7r stacking interactions present in the crystal lattice. In particular, intermolecular N-H. ..0 H-bonds were found to cause significant twisting of theo-N02 groups from the plane of the benzene ring, whereas overlapping of the picrate ions due to electrostatic interactions and 7r-7r stacking caused flattening of the molecule. Analysis of the geometry of 74 picrate ions found in the Cambridge Crystallographic Database, in their variouscrystallochemical environ- ments, showed that competition between essentially weak but numerous intermolecular interactions of different types led to systematic changes in geometric parameters within the picrate ion. In particular, relations found between the CI-C2-N-0 (CI~C6-N-0) torsion angle and the endocyclic Cl-C2-C3 (CI-C6-C5)valence angle can be explained on the basis of competition between resonance effects of the o-N02 group and 7r-7r sta5king.