6-Bromo-3-butyl-2-(4-chlorophenyl)-3H-imidazo[4,5-b]pyridine and its 4-butyl regioisomer: synthesis and analysis of supramolecular assemblies

Two regioisomers obtained from the same reaction and differing in the position of an n-butyl substituent, i.e. on either an imidazoyl-N ( 2 ) or a pyridyl-N ( 3 ), have been characterised. Different electronic structures are evident, especially in key bond lengths and angles in the imidazoyl and pyridyl rings, as discerned by X-ray crystallography, and by geometry-optimisation, natural bonding orbital and electrostatic potential charge calculations. The distinctive molecular packing in their crystals has been confirmed by Hirshfeld surface analysis as well as by interaction energy and energy framework calculations. These differences notwithstanding, the calculated lattice energies indicate very similar stabilisation between the molecules in their crystals, i.e. −101.3 and −103.5 kJ/mol for 2 and 3 , respectively, consistent with their similar calculated molecular volumes (376.8 cf. 374.1 Å 3 ), packing coefficients (69.0 cf. 69.5 %) and crystal densities (1.575 cf. 1.586 g/cm 3 ).