[X-ray crystallographic analysis of picrates].

Picric acid forms stable picrates with various organic molecules through pi- bonding or ionic bonding, and such picrates have been very useful for identification and qualitative analysis. As it seemed desirable to determine the crystal structures and the bonding mode of picrates of basic organic compounds, we have investigated the crystal structures of aromatic hydrocarbons, aromatic amino compounds, heterocyclic compounds and so on. A series of our studies on the crystal structure of basic organic compounds have shown that the complexes of picric acid and aromatic hydrocarbons are formed through pi-bonding, and those of aromatic heterocyclic compounds are formed through ionic and hydrogen bonding; in addition, some of them also have pi-bonding.