Molecular tectonics.: Porous hydrogen-bonded networks built from derivatives of pentaerythrityl tetraphenyl ether

The symmetric four-armed geometry of pentaerythrityl tetraphenyl ether (5) makes it a valuable starting point for building complex molecular and supramolecular structures. In particular, it provides a core to which multiple sites of attractive intermolecular interaction can be attached, thereby creating compounds predisposed to form complex networks by association. To facilitate exploitation of the pentaerythrityl tetraphenyl ether core in such ways, we have prepared more than 20 new derivatives by efficient methods. Of special interest are compounds 3 and 4, which incorporate four diaminotriazine groups attached to the meta and para positions of the pentaerythrityl tetraphenyl ether core. Crystallization of compounds 3 and 4 from DMSO/dioxane is directed by hydrogen bonding of the diaminotriazine groups according to well-established motifs, thereby producing three-dimensional networks. In forming these networks, each molecule of compound 3 forms a total of 12 hydrogen bonds with six others, whereas each molecule of compound 4 forms a total of 16 hydrogen bonds with four others. Both networks are highly porous and define significant interconnected channels for the inclusion of guests. In crystals of compounds 3 and 4, the fraction of the volume accessible to guests is 66% and 57%, respectively. In both cases, the pentaerythrityl tetraphenyl ether cores adopt conformations that deviate substantially from tetrahedral geometry. It is noteworthy that the inherent flexibility of the core does not favor the formation of close-packed guest-free structures.