Role of Solvent Decomposition in the Synthesis and Composition of Porous Zirconium-Based Coordination Cages

Abstract

Porous zirconium-based coordination cages are promising materials for applications in gas adsorption, catalysis, and molecular separation due to their tunability and stability. However, their synthesis is often complicated by the formation of competing phases, including insoluble or poorly soluble byproducts that impact purity and composition. Moreover, product composition and solubility can vary widely due to factors such as humidity, seasonal fluctuations, and lab-to-lab variations, highlighting the inherent lack of robustness in these syntheses. In this work, we investigate how solvothermal synthesis conditions, particularly temperature and solvent decomposition, influence the formation and composition of these cages. We show that elevated temperatures accelerate solvent breakdown, leading to the incorporation of formate and acetate byproducts that alter the final cage structures and contribute to the formation of insoluble zirconium-based, amorphous solids. By systematically varying the reaction conditions, we optimized the composition of the isolated cage products, achieving improved phase purity. By optimizing synthetic parameters, we achieve control over cage formation and particle morphology while mitigating the effects of solvent decomposition. Our findings provide insights into the balance between ligand coordination and solvent effects, enabling the development of strategies to enhance the purity, porosity, and functionality of these molecular cages.