Nanoporous molecular sandwiches: Pillared two-dimensional hydrogen-bonded networks with adjustable porosity

Crystal engineering of molecular materials is commonly frustrated by the absence of reliable structural paradigms that are needed for systematic design of crystal lattices with predictable structure and desirable function. This problem can be attributed, at least partially, to the absence of robust supramolecular motifs that serve as synthons for the assembly of crystal lattices. A novel class of molecular crystals based on two-dimensional hydrogen (H)-bonded networks comprising guanidinium ions and the sulfonate groups of alkane- or arenedisulfonate ions is described. The disulfonate ions act as pillars that connect opposing H-bonded sheets and form nanoporous galleries with one-dimensional channels. The flexibility of the H-bonded network allows the galleries to adapt to changes in the steric requirements of guest molecules that occupy the channels. This robustness reduces crystal engineering to the last remaining dimension, enabling rational adjustment of the gallery heights by choice of the disulfonate pillar.