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

Abstract

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- a]benzimidazole-8,9-diones, weak interactions were investigated by single-crystal X-ray and ¹H NMR spectroscopy methods. Crystallization of quinone derivatives containing a –NH–CH ₂– fragment led to the formation of both chiral and achiral crystals. The presence of two forms with ( endo form) and without ( exo form) an intramolecular hydrogen bond was experimentally detected by X-ray crystallography analysis and variable-temperature (VT) ¹H NMR experiments in the cases of isopentylamino- and benzylamino-substituted derivatives. Interestingly, the exo form dominates both in the solid state and in solution.