Controlling the Crystallization of Porous Organic Cages: Molecular Analogs of Isoreticular Frameworks Using Shape-Specific Directing Solvents

Small structural changes in organic moleculescan have a large influence onsolid-state crystal packing, and this often thwarts attempts to produce isostructuralseries of crystalline solids. For metal-organic frameworksand cova-lent organic frameworks, this has been addressed byusing strong,directional intermolecular bonding to create families of isoreticular solids. Here we show that an organic directing solvent, 1,4-dioxane, has a dominant effect on the lattice ener-gy for a series of organic cage molecules. Inclusion of dioxane directs the crystal packing for these cages awayfrom theirlowest-energy polymorphsto form isostructural, 3-dimensional diamondoid pore channels. This is a unique function of the size, chemical function, and geometry of 1,4-dioxane, and hence a non-covalent auxiliary interaction assumesthe role of directional coordination bonding or covalent bonding in extended crystalline frameworks. For a new cage, CC13, a dual, interpenetrating pore structure is formed which doubles the gas uptake and the surface area in the resulting dioxane-directed crystals