Investigation of Weak Noncovalent Interactions Directed by the Amino Substituent of Pyrido- and Pyrimido-[1,2-]benzimidazole-8,9-diones.

Quinones are small redox-active molecules that are able to form intra- and intermolecular interactions both in the solid state and in solution. On the basis of 6-amino-substituted pyrido- and pyrimido-[1,2-]benzimidazole-8,9-diones, weak interactions were investigated by single-crystal X-ray and H NMR spectroscopy methods. Crystallization of quinone derivatives containing a -NH-CH- fragment led to the formation of both chiral and achiral crystals. The presence of two forms with ( form) and without ( form) an intramolecular hydrogen bond was experimentally detected by X-ray crystallography analysis and variable-temperature (VT) H NMR experiments in the cases of pentylamino- and benzylamino-substituted derivatives. Interestingly, the form dominates both in the solid state and in solution.