Crystal structure of (1S,4S)-2,5-diazoniabicyclo[2.2.1]heptane dibromide

Abstract

The cage of 2,5-diazabicyclo[2.2.1]heptane is frequently employed in synthetic chemistry as a rigid bicyclic counterpart of the piperazine ring. The 2,5-diazabicyclo[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-diazabicyclo[2.2.1]heptane itself, has not been structurally characterized. We herein report on the molecular structure of the parent ring in (1S,4S)-2,5-diazoniabicyclo[2.2.1]heptane dibromide, C5H12N22+·2Br−. The asymmetric unit contains two crystallographically independent cages of 2,5-diazabicyclo[2.2.1]heptane. Each cage is protonated at the two nitrogen sites. The overall charge balance is maintained by four crystallographically independent bromide ions. In the crystal, the components of the structure are linkedviaa complex three-dimensional network of N—H...Br hydrogen bonds.