Crystal structures of di- and tri-hydrochlorides of 1,4,7-triazaheptane

Four protonated 1,4,8,11-tetraazacyclotetradecane has been characterized as nitrates to show expanded ring structure due to charge repulsion[1]. However, linier polyamine, 1,4,7-triazaheptane (diethylentriamine=dien) gave di-hydrochloride(1) and tri-hydrochloride(2) and their single crystal structures were examined. In the compound 1, the terminal N atoms are protonated as expected but the dien takes U-shaped conformation with forming double H-bond to a Cl- ion at the terminals and the central nitrogen forms another H-bond to the other Cl- ion, as shown in the figure. The dien takes linear conformation in the compound 2 as expected.