Crystal engineering strategies in alkane-bis(ammonium) 2,5-diaza-3,6-dioxobicyclo[2.2.2]octane-1,4-dicarboxylates

The crystal structures of (+)-3, (±)-4 and P-(–)-5 were studied; the competitive H-bonding of carboxylic groups in (+)-3 and (±)-4 leads to disruption of crystal structure elements, used previously in crystal engineering of chiral bis(lactams); the new structure elements may be described as 1D homochiral R22(10) tapes; the diastereomeric resolution in P-(–)-5 is rationalised using an analogy between the H-bonded structure of the salt and 2,5-diaza-3,6-dioxobicyclo[2.2.2]octane-1,4-dicarboxylic acid dihydrate.