Structural characterization and chemical response of a Ag-coordinated supramolecular gel

Supramolecular gels exhibit potential applications in the areas of sensors, nanodevices, drug and catalyst carriers, and so on. To develop a novel organogel with a multiresponse, we designed a component molecule bearing a pyridyl group for metal coordination and an amide group for the formation of intermolecular hydrogen bonding. A complex building block with a symmetrical structure was selectively constructed by the coordination of a silver cation to the organic component. The coordination existing in the complex and the hydrogen bonding existing between complexes were examined by IR, Raman, and H-1 NMR spectroscopy. The gel formation and phase transition were examined by viscosity and differential scanning calorimetry measurements. The selection of metal ions for the formation of a gel has proved to be crucial as only the complex of a binary coordinated metal ion, Ag+, was found to form a gel structure. From the band shift of the L1 solution with different amounts of silver ion, the binding ratio of silver ion to L1 was estimated to be 1:2 and the calculated stability constant was 3.6 x 10(8) M-2. On the basis of the analysis of X-ray diffraction and transmission electron microscopy results, we proposed a possible stacking structure of the complex in the fibrous aggregates. Of interest is that the organogel exhibits a 3-D network structure of a beltlike fiber composed of ordered lamellar arrangements of the coordinated complex and shows a rapid response to wide chemical stimulations such as anions I-, Br-, and Cl-, gases such as H2S and NH3, and a change of pH.