“Crystal Engineering” with Two-Dimensional Hydrogen Bonding Networks

Abstract

One approach toward controlling the assembly of molecules into predictable crystalline architectures involves the use of higher dimensional supramolecular networks that are resilient toward changes in ancillary functional groups attached to molecular constituents of the network. The use of n-dimensional networks facilitates the design and synthesis of new materials by reducing crystal engineering to 3-n dimensions. We describe herein the assembly of adjustable and highly porous host lattices based on robust two-dimensional guanidinium-sulfonate hydrogen bonded networks. The resilience of this network allows facile prediction of crystal structure, including architectural isomers that can be directed by judicious choice of guest molecules in solution. Two architectural isomers, a pillared bilayer form and a pillared brick form, have substantial porosity that is sustained by a diverse variety of guest molecules. Notably, the brick frameworks have packing fractions (without guest), nominally twice that of the bilayer materials. Molecular host lattices with nanometer scale porosity provide substantial opportunities in areas including crystallization-based chemical separations, synthesis of new functional materials, and topochemically-directed reactions.