Crystal packing of two 5-substituted 2-methyl-4-nitro-1H-imidazoles

Infinite chains connected by N-H...N hydrogen bonding form the primary packing motif in two closely related 4-nitroimidazole derivatives, viz. 5-bromo-2-methyl-4-nitro-1H-imidazole, C4H4BrN3O2, (I), and 2-methyl-4-nitro-1H-imidazole-5-carbonitrile, C5H4N4O2, (II). These chains are almost identical, even though in (II) there are two symmetry-independent molecules in the asymmetric unit. The differences appear in the interactions between the chains; in (I), there are strong C-Br...O halogen bonds, which connect the chains into a two-dimensional grid, while in (II), the cyano group does not participate in specific interactions and the chains are only loosely connected into a three-dimensional structure.