Co-crystallization of a benzimidazole derivative with carboxylic acids

The co-crystallization of a benzimidazole derivative (1, C27H26N6O3, 3-[[[2-[[(4-Cyanophenyl) amino]methyl]-1-methyl-1H-benzimidazol-5-yl]carbonyl]pyridin-2-ylamino]propionic acid ethyl ester), with fumaric acid (FA) and maleic acid (MA), has been performed. The FA and MA molecules, both are connected with two molecules of C27H26N6O3, giving birth to a three-components compound (1·0.5FA, C29H28N6O5) and a four-components compound (1·MA, C31H30N6O7). Single-crystal X-ray diffractions show that the three different planar moieties (4-cyanophenyl, benzimidazol, and pyridin-2-yl) in compound C27H26N6O3 display “cis-form” conformation (a) in the crystal of 1, while exhibiting “intermediate-state” conformation (b) and “trans-form” conformation (c) in compounds 1·0.5FA and 1·MA, respectively. Hirshfeld surfaces analysis, DFT calculations, DSC measurements, IR and Raman spectroscopy were performed, which revealed that the thermal stability of the three conformations follows the order c > b > a.