This article reports studies on benzimidazole based heterocyclic compounds (S3 -S5). X-ray diffraction technique was applied to study the structure of (C23H19N4O2)(+).Br-.H2O, namely 1-[(2-cyanophenyl) methyl]-3-[2-(4-nitrophenyl)ethyl]-1H-benzimidazol-3-ium bromide monohydrate (S3). The molecules are linked by C-H/Br hydrogen bonds in the crystal and there are pi-pi stacking interactions between the centroids of the benzene ring in the benzimidazole nucleus. The theoretical, and chemical data of S3-S5 were compared with experimental calculations via NMR, IR, and UV-Vis spectra of the molecules. Afterwards, the biological activities of the molecules were compared against colon cancer antigen pro-teins, ID 2HQ6, and a breast cancer protein, which is a crystal structure of a dimeric caspase-9, ID 2AR9. Experimental and theoretical studies have shown that the biological activity of the molecule S5 is higher than that of other molecules. (C) 2020 Elsevier B.V. All rights reserved.