Engineering Hydrogen-Bonded Molecular Crystals Built from Derivatives of Hexaphenylbenzene and Related Compounds

Hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (4) incorporates a disc-shaped hexaphenylbenzene core and six peripheral diaminotriazine groups that can engage in hydrogen bonding according
to established motifs. Under all conditions examined, compound 4 crystallizes as planned to give closely
related noninterpenetrated three-dimensional networks built from sheets in which each molecule has six
hydrogen-bonded neighbors. In the structure of compound 4, the number of hydrogen bonds per molecule
and the percentage of volume accessible to guests approach the highest values so far observed in molecular
networks. Analogue 5 (which has the same hexaphenylbenzene core but only four diaminotriazine groups
at the 1,2,4,5-positions) and analogue 7 (in which the two unsubstituted phenyl groups of compound 5 are
replaced by methyl groups) crystallize according to a closely similar pattern. Analogues with flatter
pentaphenylbenzene or tetraphenylbenzene cores crystallize differently, underscoring the importance of
maintaining a consistent molecular shape in attempts to engineer crystals with predetermined properties.