Guanidinium and organosulfonate ions self-assemble into two- dimensional hydrogen bonding networks with the general formula [C(NH2>3]+ RSO3" having pseudo-hexagonal symmetry due to hydrogen bonding between six guanidinium proton donors and six sulfonate electron lone pair acceptors. These hydrogen bonded layers assemble in tlie third dimension in a manner which maximizes van der Waals interactions between R groups. The steric requirements of the R groups dictate whether this assembly results in "classical" bilayer motifs in which all the R groups are oriented to one side of a given sheet or "single layer" motifs in which R groups are oriented to both sides of a given hydrogen-bonded sheet. Synthesis and characterization of over 30 crystalline compounds reveal that this hydrogen-bonded network is robust, which aids significantly in materials design as tlie crystal engineering problem is reduced to one dimension. The pervasiveness of this network can be attributed to the "softness" of hydrogen-bonding which allows the sheets to pucker slightly in order to accomodate steric strain between R groups within tlie layers. Identical networks have also been synthesized from a,co-alkanedisulfonates and aromatic disulfonates in which the hydrogen-bonded sheets are pillared by organic spacers and the hydrocarbon density between layers is reduced by a factor of two compared to tlie monosulfonate analogs. This leads to nanoporous "molecular sandwiches" in which tlie void space can be controlled simply by adjusting the structure of tlie organic pillar, suggesting rational design of host-guest compounds.
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