The frameworks engineered by the University of Minnesota's Ward and coworkers Jennifer A. Swift, Adam M. Pivovar, and Anne M. Reynolds are based on extended, flexible sheets in which guanidinium cations (green) are hydrogen-bonded to sulfonate (SO₃^-) groups (yellow) attached to an organic moiety (red). Depending on the size of their organic substituent, the organomonosulfonates form either a bilayer or a continuously interdigitated architecture. When organodisulfonates are used, these molecules serve as "pillars," connecting pairs of hydrogen-bonded sheets. The pillared architectures contain voids that can be filled with guest molecules (blue). Actual examples of guanidinium 4,4'-biphenyldisulfonate clathrates are shown, with naphthalene guests in the pillared bilayer (top right) and 1,4-divinylbenzene guests in the pillared brick architecture (bottom right). In the latter case, the presence of the larger guest molecule forces the formation of the brick.