Crystal structure and homopolar dihydrogen interactions in propano‐bridged indigo.

Single crystal X‐ray crystallographic analysis of 7,8‐dihydro‐6H‐[1,4]diazepino[1,2‐a:4,3‐a′]diindole‐14,15‐dione (propano‐bridged indigo [PBI]) reveals the presence of two homopolar intermolecular dihydrogen C–H···H–C interactions of distances 2.38 and 2.89 Å. Hirshfeld surface analysis indicates a significant contribution of C–H···H–C interactions (49%) to the total molecular contact surface. Theoretical analysis of the topology of electron density reveals the existence of two closed shell dihydrogen interactions per dimer. The values of the AIM charges on the H⋯H interacting atoms are similar (0.172). The calculated dihydrogen interaction energy is found to be significant (3.76 kcal mol−1). London dispersion forces are the dominant contributor to the homopolar C–H···H–C interactions. [ABSTRACT FROM AUTHOR]