Crystal structures of pure 3-(4-bromo-2-chloro-phen-yl)-1-(pyridin-4-yl)benzo[4,5]imidazo[1,2- d ][1,2,4]triazin-4(3 H )-one and contaminated with 3-(4-bromo-phen-yl)-1-(pyridin-4-yl)benzo[4,5]imidazo[1,2- d ][1,2,4]triazin-4(3 H )-one

The side product of the cyclo-condensation reaction between ethyl benzimidazole-2-carboxyl-ate and the nitrile imine of the corresponding hydrazonyl chloride, C H BrClN O, crystallized in two crystal forms. Form ( ) is a co-crystal of the target compound (without any chlorine substituent) and a side product containing a Cl atom in position 2 of the bromo-phenyl group, C H BrN O·0.143C H BrClN O. ( ) contains the pure side product. The slightly different conformation of the ring systems leads to a different packing of ( ) and ( ), but both crystal structures are dominated by π-π inter-actions.