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

Abstract

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.