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.

季戊四醇四苯基醚（pentaerythrityl tetraphenyl ether，化合物5）具有对称的四臂几何结构，是构建复杂分子与超分子结构的极具价值的合成起始砌块。尤为重要的是，该分子可作为核心骨架，连接多个可参与分子间相互作用的位点，从而得到易于通过分子间组装形成复杂网络的化合物。为便于利用此类季戊四醇四苯基醚核心开展相关研究，我们通过高效合成方法制备了二十余种新型衍生物。其中化合物3与4尤为引人关注：二者均在季戊四醇四苯基醚核心的对应位置连接了四个二氨基三嗪（diaminotriazine）基团——化合物3的基团连接于间位，化合物4的基团连接于对位。将化合物3与4从二甲基亚砜（DMSO）/二氧六环（dioxane）混合溶剂中结晶时，二氨基三嗪基团的氢键作用可依照公认的经典基序引导晶体生长，最终形成三维网络结构。在形成此类网络的过程中，每个化合物3分子可与其余6个分子共计形成12条氢键，而每个化合物4分子则可与其余4个分子共计形成16条氢键。两种网络均具备高孔隙率，且形成了大量相互连通的孔道以容纳客体分子。在化合物3与4的晶体中，客体可及体积分数分别为66%与57%。在两种体系中，季戊四醇四苯基醚核心的构象均与标准四面体几何结构存在显著偏差。值得注意的是，该核心固有的柔性并不利于形成紧密堆积的无客体晶体结构。