Post-Synthetic Modification of Aerogels Made of Covalent Cross-linked Metal-Organic Polyhedra

Aerogels are porous ultralight materials known for their high porosity, wide range of pore sizes, low density, and good macroscopic mechanical properties, all of which make them promising candidates for shaped adsorbents, catalysts, and insulators, among other applications. Here, this work reports a new approach that enables both the formation of modular aerogels, via dynamic covalent chemistry, and their post-synthetic modification, via coordination chemistry. To demonstrate this strategy, this work first polymerizes porous amino-functionalized Rh(II)-based metal-organic polyhedra (MOPs) with aldehydes, which afforded robust imine-gel networks that is then converted into aerogels. Next, this work functionalizes these aerogels through the coordination of ligands on the axial site of Rh(II) paddlewheels of the MOP. Interestingly, in this chemistry, the local changes in the coordination site of the MOPs are transferred to the overall aerogel, thereby altering its macroscopic physicochemical properties. Importantly, this feature enables the synthesis of optimized adsorbents tailored to specific guests, as this work demonstrates through a series of experiments using ligands of different electrostatic and hydrophobic characters. This study presents a methodology for the synthesis of robust MOP-based aerogels via covalent chemistry, and their post-synthetic functionalization through coordination chemistry. The latent reactivity on the outer metal-open sites of the Rh(II)-based MOPs is used to post-synthetically modify the macroscopic physicochemical properties of the aerogel toward the development of optimized adsorbents for targeted guests.image