Toward the Design of Porous Organic Solids: Modular Honeycomb Grids Sustained by Anions of Trimesic Acid

摘要

The concept of design or crystal engineering of functional solids relies upon controlling the topology of crystal packing through exploitation of forces that range in the continuum from weak hydrogen bonds to covalent bonds. In the context of porosity, a particularly relevant functional property given the commercial importance of zeolites, it is becoming increasingly clear that even noncovalent interactions can be directional and strong enough to generate and sustain porosity. Several research groupshave recently demonstrated that a modular strategy to crystal engineering can propagate molecular symmetry into crystalline architecture or even space group symmetry. Unfortunately, two- (2D) and three-dimensional (3D) frameworks typically fail to realize their full potential for porosity because of interpenetration or self-inclusion of identical frameworks. In such a context, trimesic acid (1,3,5-benzenetri-carboxylic acid, H_3TMA) is prototypal since it predictably self-assembles through the well-known carboxylic acid dimer motif into an interpenetrating honeycomb grid with 11 A cavities. We report herein on two compounds that illustrate two alternate modular strategies to propagate the trigonal symmetry of H_3TMA: the ammonium salt I forms a neutral honeycomb grid and the ammonium salt 2 has an anionic honeycomb grid based upon hydrogenbiscarboxylate hydrogen bonds.