Engineering Hydrogen-Bonded Hexagonal Networks Built from Flexible 1,3,5-Trisubstituted Derivatives of Benzene

2,4-Diamino-1,3,5-triazinyl
(DAT) groups are known to form N–H···N
hydrogen bonds according to reliable patterns of self-association.
In compounds 3a–c, three DAT groups
are attached to trigonally substituted phenyl cores via identical
flexible arms. Crystallization of compounds 3a–c produces robust networks in which each molecule is linked
to its immediate neighbors by a total of 10–12 hydrogen bonds.
In compound 3a, the DAT groups are designed to lie close
to the plane of the phenyl core, thereby giving hydrogen-bonded sheets
built from hexameric rosettes. In contrast, the more highly substituted
phenyl cores of analogues 3b and 3c favor
conformations in which the DAT groups are no longer coplanar, leading
predictably to the formation of three-dimensional networks. In general,
the nominally trigonal topologies of compounds 3a–c favor structures in which hexagonal networks are prominent,
so they behave like trimesic acid despite their greater complexity
and flexibility. The structures of all crystals incorporate open networks
with significant fractions of volume accessible to guests (32–60%).
Despite their flexibility, compounds 3a–c appear to be unable to assume conformations that pack efficiently
and simultaneously allow the DAT groups to engage in normal hydrogen
bonding.