4,7-Diaza-1-azoniacyclo-nonane bromide.

The title compound, C(6)H(16)N(3) (+)·Br(-), is the bromide of the monoprotonated aza-macrocyclic triamine 1,4,7-triaza-cyclo-nonane (tacn). The threefold axis of the triamine is broken by the protonation of one of the three amine functions. The ammonium proton is bonded in an intra-molecular symmetrically bifurcated hydrogen bond to the two endodentate amine functions. Direct cation-anion contacts are established via N-H⋯Br hydrogen bonds between the bromide anions and tacnH(+) cations.