Static and Dynamic Adsorptions of Water Vapor by Cyclic [Zr36] Clusters: Implications for Atmospheric Water Capture Using Molecular Solids

A 36‐nuclear Zr(IV) cluster based on six [Zr6O4(OH)4] units is found to form three different crystal structures depending on synthesis conditions. The cubic phase (ZF‐3c) is obtained when the cyclic clusters are interlinked by Na+ or K+ ions. In the absence of alkali metal ions, either tetragonal (ZF‐3t) or hexagonal (ZF‐3h) packing structures are formed. All the solids remain crystalline after evacuation, and ZF‐3h possesses a permanent porosity. Upon repeated adsorptions of water vapor, the three different molecular solids comprising the same building blocks turn amorphous; however, overall uptake properties are not deteriorated and reproducible isotherms are observed featuring fast uptake at low relative humidity and unrestricted uptake at RH > 90%. A good reproducibility has also been established in cyclic adsorption–desorption measured under dynamic flow conditions, and, especially ZF‐3t displays the working capacity 2.7 times that of zeolite 4A thanks to the fast desorption kinetics.