Crystal structure and halogen-hydrogen bonding of a Delépine reaction inter-mediate.

The reaction of 1,5-di-bromo-pentane with urotropine results in crystals of the title mol-ecular salt, 5-bromo-urotropinium bromide [systematic name: 1-(5-bro-mo-pent-yl)-3,5,7-tri-aza-1-azoniatri-cyclo-[3.3.1.1(3,7)]decane bromide], C(11)H(22)BrN(4) (+)·Br(-) (1), crystallizing in space group P2(1)/n. The packing in compound 1 is directed mainly by H⋯H van der Waals inter-actions and C-H⋯Br hydrogen bonds, as revealed by Hirshfeld surface analysis. Comparison with literature examples of alkyl-urotropinium halides shows that the inter-actions in 1 are consistent with those in other bromides and simple chloride and iodide species.