Self-assembly of cage structures. Paper 12: The synthesis and crystal structures of 2,5-diazabicyclo[2.2.2]octane-3,6-dione-1,4-dicarboxylic acids and their diesters

Synthesis of racemic and enantiomeric 2,5-diazabicyclo[2.2.2]octane-3,6-dione-dicarboxylic acids and their diesters, as functionalized building blocks for supramolecular chemistry, is described. It is shown that heterochiral H-bonded zigzag tape with R22(8) graph and molecular ‘brick wall’ with a non-polar coating are persistent and stable motifs in the crystal structures of the racemic dialkyl 2,5-diazabicyclo[2.2.2]octane-3,6-dione-1,4-dicarboxylates (, , ). This stability was confirmed by quasi-racemate · formation and crystal structure determination. Packing of the diacids and dihydrates differed from that of esters, with H2O molecules linking homochiral spirals, into corrugated homochiral layers, observed in both structures. The crystal structure of enantiomeric diester contained spirals similar to those observed in diacids with participation of the ester carbonyl groups in H-bonding.