Nanosheets and Hydrogels Formed by 2 nm Metal–Organic Cages with Electrostatic Interaction
Yuqing Yang, Pavel Řehák, Ting‐Zheng Xie, Yi Feng, Xinyu Sun, Jiahui Chen, Hui Li, Petr Král, Tianbo Liu
Abstract
We report the mechanism of hydrogel formation in dilute aqueous solutions (>15 mg/mL) by 2 nm metal-organic cages (MOCs). Experiments and all-atom simulations confirm that with the addition of small electrolytes, the MOCs self-assemble into 2D nanosheets via counterion-mediated attraction because of their unique molecular structure and charge distribution as well as σ-π interactions. The stiff nanosheets are difficult to bend into 3-D hollow, spherical blackberry type structures, as observed in many other macroion systems. Instead, they stay in solution and their very large excluded volumes lead to gelation at low (∼1.5 wt %) MOC concentrations, with additional help from hydrophobic and partial π-π interactions similar to the gelation of graphene oxides.