INDUCTION OF NONCENTROSYMMETRY BY POLAR HYDROGEN-BONDED CHAINS IN NITROANILINE CRYSTALS

The role of polar hydrogen-bonded nitroaniline chains in inducing noncentrosymmetry in bulk nitroanilines is explored here using correlations between the presence of such motifs and the occurrence of noncentrosymmetric space groups among all known nitroaniline crystal structures. Our results show a significant bias for compounds with polar nitroaniline motifs to have noncentrosymmetric structures (46% of 24 structures) compared to the frequency with which achiral molecules in general form noncentrosymmetric crystal structures (11%). Thus, the special role that nitroanilines have played in the field of organic nonlinear optical materials may be attributed not just to their normally large hyperpolarizabilities but also to the fact that this class of molecules has an unusually high tendency to form noncentrosymmetric crystals.