Bispicolyamine-Based Supramolecular Polymeric Gels Induced by Distinct Different Driving Forces with and Without Zn2+

Abstract

Metal-coordination polymeric gels are interesting areas as organic/inorganic hybrid supramolecular materials. The bispicolylamine (BPA) based gelator (1) showed excellent gelation with typical fibrillar morphology in acetonitrile. Upon complexing1with Zn2+, complexes ([1+ Zn + ACN](2+)and [1+ zinc trifluoromethanesulfonate (ZnOTf)](+)) with four coordination numbers were formed, which determine the gel structure significantly. A gel-sol transition was induced, driven by the ratio of the two metal complexes produced. Through nuclear magnetic resonance analysis, the driving forces in the gel formation (i.e., hydrogen-bonding and pi-pi stacking) were observed in detail. In the absence and the presence of Zn2+, the intermolecular hydrogen-bonds and pi-pi stacking were the primary driving forces in the gel formation, respectively. In addition, the supramolecular gels exhibited a monolayer lamellar structure irrespective of Zn2+. Conclusively, the gels' elasticity and viscosity reduced in the presence of Zn2+.