Glass Formation of a Coordination Polymer Crystal for Enhanced Proton Conductivity and Material Flexibility

The glassy state of a two-dimensional (2D) Cd²⁺ coordination polymer crystal was prepared by a solvent-free mechanical milling process. The glassy state retains the 2D structure of the crystalline material, albeit with significant distortion, as characterized by synchrotron X-ray analyses and solid-state multinuclear NMR spectroscopy. It transforms to its original crystal structure upon heating. Thus, reversible crystal-to-glass transformation is possible using our new processes. The glass state displays superior properties compared to the crystalline state; specifically, it shows anhydrous proton conductivity and a dielectric constant two orders of magnitude greater than the crystalline material. It also shows material flexibility and transparency. Phase transitions: The glassy state of a two-dimensional (2D) Cd²⁺ coordination polymer crystal was prepared by a solvent-free mechanical milling process. The coordination polymer shows an increased proton conductivity and an increased dielectric constant in the glassy state (see picture).