Journal of Physical Chemistry A, Vol.106, No.29, 6897-6903, 2002
Charge density studies of weak interactions in dipicrylamine
A low-temperature high-resolution X-ray and neutron diffraction study of charge distribution in the superacid dipicrylamine (DPA) has been carried out. This structure exhibits interesting weak interactions including bifurcated N-(HO)-O-... and C-(HO)-O-... H-bonds which consolidate it. The corresponding interaction lines appear to be modified in the vicinity of the critical points of the covalent bonds of the hydrogen atoms. The presence of six nitro groups generates some short (NO)-O-... contacts. On the basis of the experimental interaction paths, an attractive interaction is found, in agreement with the prediction of such an effect from earlier model ab initio calculations performed for simple dimers. For these weak interactions, a linear relationship is found between the charge density at the interaction critical points and the N-O distance.