Architectural isomerism and inclusion behavior of guanidinium organosulfonates

The development of functional molecular materials requires precise control over crystal packing due to the relationship between macroscopic properties and three-dimensional structure. Intermolecular interactions such as hydrogen bonds often exert a strong directional influence on the self-assembly of molecules and aid in defining the solid-state structures of molecular crystals. Guest-free guanidinium monosulfonate (GMS) compounds and GMS inclusion compounds display a variety of lamellar crystalline architectures characterized by different "up-down" arrangements of the organomonosulfonate "posts" with respect to a two-dimensional hydrogen-bonded network of complementary guanidinium ions (G) and sulfonate moieties (S), the so-called GS sheet. The GMS compounds exhibit a marked propensity to incorporate a variety of guest molecules through variations in the connectivity of the two-dimensional GS sheet. These architectures exhibit sheet topologies identical to those previously observed in guanidinium disulfonate (GDS) compounds, as well as new topologies that exemplify the capacity to achieve nearly unlimited structural arrangements. The architectures observed in the GMS inclusion compounds possess greater structural freedom than those observed for guest-free GMS compounds, as the dual requirements of a flat GS sheet and strict intersheet registry are no longer enforced. The ability to form inclusion compounds with a large range of guest molecules results from the additional degree of freedom associated with the ability of adjacent sheets to float independently of one another and allows the host to conform to the steric demands of the included guest, providing the necessary enthalpic driving force for the formation of stable inclusion compounds. The ability of GDS compounds to perform shape selective separations of molecular isomers was also investigated. Rigid frameworks exhibited limited selectivity compared to flexible frameworks that were able to conform to the different steric requirements of guest molecules.