Polymorphs of DABCO monohydrate as structural analogues of NaCl.

A new crystalline form of 1,4-diazabicyclo[2.2.2]octane (DABCO) monohydrate, C(6)H(12)N(2).H(2)O, crystallizing in the space group P3(1), has been identified during screening for cocrystals. There are three DABCO and three water molecules in the asymmetric unit, with two DABCO molecules exhibiting disorder over two positions related by rotation around the N...N axis. As in the monoclinic C2/c (Z' = 2) polymorph, the molecular components are connected via O-H...N hydrogen bonds into a polymeric structure that consists of linear O-H...N(CH(2)CH(2))(3)N...H-O segments, which are approximately mutually perpendicular. The two polymorphic forms of DABCO monohydrate can be considered as structural analogues of NaCl, with the nearly globular DABCO molecules showing distorted cubic closest packing and all octahedral interstices occupied by water molecules.