High-Concentration Self-Assembly of Zirconium- and Hafnium-Based Metal-Organic Materials

摘要

Metal-organic frameworks (MOFs) are crystalline,poroussolids constructed from organic linkers and inorganic nodes that arepromising for applications in chemical separations, gas storage, andcatalysis, among many others. However, a major roadblock to the widespreadimplementation of MOFs, including highly tunable and hydrolyticallystable Zr- and Hf-based frameworks, is their benchtop-scalable synthesis,as MOFs are typically prepared under highly dilute (<= 0.01 M)solvothermal conditions. This necessitates the use of liters of organicsolvent to prepare only a few grams of MOF. Herein, we demonstratethat Zr- and Hf-based frameworks (eight examples) can self-assembleat much higher reaction concentrations than are typically utilized,up to 1.00 M in many cases. Combining stoichiometric amounts of Zror Hf precursors with organic linkers at high concentrations yieldshighly crystalline and porous MOFs, as confirmed by powder X-ray diffraction(PXRD) and 77 K N-2 surface area measurements. Furthermore,the use of well-defined pivalate-capped cluster precursors avoidsthe formation of ordered defects and impurities that arise from standardmetal chloride salts. These clusters also introduce pivalate defectsthat increase the exterior hydrophobicity of several MOFs, as confirmedby water contact angle measurements. Overall, our findings challengethe standard assumption that MOFs must be prepared under highly dilutesolvothermal conditions for optimal results, paving the way for theirscalable and user-friendly synthesis in the laboratory.