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The synthesis of Ce-fumarate and Zr-fumarate metal-organic framework (MOF) is monitored for the first time with in situ Raman spectroscopy in custom-built solvothermal reactors. Several synthesis conditions were explored for Ce-fumarate at room temperature. The use of the method for high-temperature synthesis of Zr-fumarate is also demonstrated. In situ Raman monitoring provided insights into both the solution and crystalline phases of the reaction medium, revealing the dynamic interplay among precursors, modulators, and the forming MOF structure. The reaction kinetics was determined by following the characteristic peak at 1666 cm -1 . The conversion was in good agreement with the reaction kinetics determined via in situ synchrotron powder diffraction. The resulting MOF products were further characterized using ex situ X-ray powder diffraction, scanning electron microscopy, thermogravimetry, and surface area measurements. This study demonstrates a simple and industrially scalable method for monitoring MOF synthesis in situ, which can provide insights into the stages and mechanisms of formation of MOFs and other compounds., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Microporous metal-organic frameworks are a class of materials being vigorously investigated for mobile hydrogen storage applications. For high-pressure storage at ambient temperatures, the M(3)[(M(4)Cl)(3)(BTT)(8)](2) (M-BTT; BTT(3-) = 1,3,5-benzenetristetrazolate) series of frameworks are of particular interest due to the high density of exposed metal cation sites on the pore surface. These sites give enhanced zero-coverage isosteric heats of adsorption (Q(st)) approaching the optimal value for ambient storage applications. However, the Q(st) parameter provides only a limited insight into the thermodynamics of the individual adsorption sites, the tuning of which is paramount for optimizing the storage performance. Here, we begin by performing variable-temperature infrared spectroscopy studies of Mn-, Fe-, and Cu-BTT, allowing the thermodynamics of H(2) adsorption to be probed experimentally. This is complemented by a detailed DFT study, in which molecular fragments representing the metal clusters within the extended solid are simulated to obtain a more thorough description of the structural and thermodynamic aspects of H(2) adsorption at the strongest binding sites. Then, the effect of substitutions at the metal cluster (metal ion and anion within the tetranuclear cluster) is discussed, showing that the configuration of this unit indeed plays an important role in determining the affinity of the framework toward H(2). Interestingly, the theoretical study has identified that the Zn-based analogs would be expected to facilitate enhanced adsorption profiles over the compounds synthesized experimentally, highlighting the importance of a combined experimental and theoretical approach to the design and synthesis of new frameworks for H(2) storage applications.