Crystal structure of (1S,4S)-2,5-diazo-niabi-cyclo[2.2.1]heptane dibromide.

The cage of 2,5-di-aza-bicyclo-[2.2.1]heptane is frequently employed in synthetic chemistry as a rigid bicyclic counterpart of the piperazine ring. The 2,5-di-azabicyclo-[2.2.1]heptane scaffold is incorporated into a variety of compounds having pharmacological and catalytic applications. The unsubstituted parent ring of the system, 2,5-di-aza-bicyclo-[2.2.1]heptane itself, has not been structurally characterized. We herein report on the mol-ecular structure of the parent ring in (1S,4S)-2,5-diazo-niabi-cyclo-[2.2.1]heptane dibromide, C5H12N22+·2Br-. The asymmetric unit contains two crystallographically independent cages of 2,5-di-aza-bicyclo-[2.2.1]heptane. Each cage is protonated at the two nitro-gen sites. The overall charge balance is maintained by four crystallographically independent bromide ions. In the crystal, the components of the structure are linked via a complex three-dimensional network of N-H⋯Br hydrogen bonds.