Low-entropy Supramolecular Crystals: Elucidating the Inhomogeneity of Interfacial Water Molecules at Atomic Resolution

Water at interfaces plays crucial roles in various natural phenomena and in the material sciences. Therefore, understanding the structure and hydrogen-bonding network at such interfaces is essential. Recent advances in porous crystalline materials, combined with single-crystal X-ray diffraction techniques, have enabled the visualization of molecular structures on pore surfaces at atomic resolution. Herein, we report the formation of a supramolecular porous crystal composed of a resorcin[4]arene and a rigid cationic coordination complex, stabilized by hydrogen bonds and noncovalent interactions. This low-entropy arrangement creates a porous framework with anisotropic, information-rich surfaces, accommodating water molecules to form multi-layered water channels. The analysis reveals clustering motifs and hydrogen-bonding patterns in the water molecules at interfaces, supported by molecular dynamics calculations and spectroscopy studies. These findings advance our understanding of the structure–property relationship of water at interfaces in lowentropy crystalline materials, offering insights into their behavior on complex surfaces.