GUANIDINIUM PARASUBSTITUTED BENZENESULFONATES - COMPETITIVE HYDROGEN-BONDING IN LAYERED STRUCTURES AND THE DESIGN OF NONLINEAR-OPTICAL MATERIALS

X-ray crystal structures of six guanidinium para-substituted benzenesulfonates, [C(NH2)3]+(p-XC6H4SO3]-X = -CH3, -NH2, -OCH3, -NO2, -OH, and -CO2H), are reported. Molecular packing in these salts is directed predominantly by hydrogen-bonding and Coulombic interactions. The planar guanidinium-sulfonate hydrogen-bonded sheet motif that is generally observed for these compounds is disrupted when the substituent X has hydrogen-bonding character. Consequently, the sheets ''pucker'' about guanidinium-sulfonate hydrogen-bonded ribbons, the puckering increasing with increasing hydrogen-bonding ability of X. For X = -CH3, -NH2, and -OCH3 the typical nearly planar sheet motif is observed. For X = -NO2 and -OH, the puckering of the hydrogen-bonded sheets is severe, and the ribbons assemble into noncentrosymmetric crystalline phases (Ama2 and Ima2, respectively) which exhibit second harmonic generation. For X = -CO2H, the sheet motif is completely disrupted due to competitive hydrogen bonding of X for guanidinium and sulfonate hydrogen-bonding sites. However, guanidinium-sulfonate hydrogen-bonded ribbons are observed in all salts. These studies suggest that the highly directing hydrogen-bonding and ionic character of the guanidinium-sulfonate networks provide a sound strategy for materials design, particularly for low-dimensional electronic properties and second harmonic generation.