Structure of a 1:1 complex between the anthelmintic drug mebendazole and propionic acid

Recrystallization of the anthelmintic drug mebendazole from propionic acid yields a 1:1 molecular complex which crystallizes in the triclinic system space group , a = 5.928(2), b = 11.066(2), c = 14.337(6)Å, = 94.89(3), = 101.56(3), = 96.18(2)°, and Z = 2 complex units in the unit cell. An x-ray diffraction study revealed an R₂²(8) hydrogen bonding system in the complex, involving the unprotonated imidazole N and amide N–H function of the drug and the acid carboxylic group. Complex molecules form centrosymmetric dimers by intermolecular N–H···O hydrogen bonding involving the protonated imidazole N atom and the benzoyl O atom of the drug molecule.