Crystal Transformation from the Incorporation of Coordinate Bonds into a Hydrogen-Bonded Network Yields Robust Free-Standing Supramolecular Membranes

In this work, we report on the synthesis of a free-standing, macroscopic robust supramolecular membrane by introducing silver–nitrogen coordinate bonding into preorganized, supramolecular hydrogen-bonded cyanuric acid-melamine (CAM) crystals. With the assistance of ammonia, silver ions competitively replace two of the three hydrogen atoms from cyanuric acid resulting in the transformation from short CAM nanorods to long CAM-Ag nanofibers (length over 1000 μm), accompanied by tautomerization of cyanuric acid. The single crystal structure of the CAM-Ag nanofibers is solved in the space group P1, with the asymmetric unit containing eight silver atoms, four melamine and four cyanuric acid molecules, which generate 1D coordination polymer chains consisting of alternating melamine and dianionic cyanurate ligands linked via silver–nitrogen bonds. The presence of interchain hydrogen bonds results in the expansion of the supramolecular network into undulating 2D sheets, which then stack into a 3D network via a ser...