In Situ Monitoring of Copper Benzenehexathiol Coordination Polymer Formation via High-Resolution Liquid-Cell Transmission Electron Microscopy

Liquid-cell transmission electron microscopy (LC-TEM) represents a promising technique for obtaining detailed knowledge about crystal nucleation and growth. For conjugated coordination polymer (c-CP) crystals, which are constructed by linking conjugated organic ligands with metal nodes, the growth mechanism remains poorly understood, making LC-TEM an ideal method to fill this gap. However, the general low stability of these materials under the electron beam has hindered high-resolution experiments. Here, we overcome this obstacle and demonstrate high-resolution LC-TEM experiments for the growth of a copper-linked benzenehexathiol (BHT) c-CP. Surprisingly, the synthesis led to the formation of Cu₄(BHT) instead of the expected Cu₃(BHT), which is found in corresponding ex-situ experiments. We attribute the formation of different structures in ex-situ and in situ experiments to radiolysis occurring during the interaction of the electron beam with the solutions inside the liquid cell, as well as the restrictions dictated by the laminar flow in the microfluidic system.

Liquid-cell transmission electron microscopy (LC-TEM) high-resolution imaging of conjugated coordination polymer (c-CP) crystal growth is demonstrated, despite the low stability of these polymers under the electron beam. Copper-linked benzenehexathiol (BHT) c-CP unexpectedly forms Cu₄(BHT) instead of Cu₃(BHT), attributed to radiolysis-induced reduction of the copper source.