Compositional Stages in the Thermal Activation of Metal-Organic Frameworks in Vacuo: In Situ Spectroscopy and Computation.

The final step in revealing the porosity of most metal-organic frameworks (MOFs), the ultimate step of the activation process, involves removal of solvent from the pores. This is commonly accomplished with the application of vacuum and heat; whereas some MOFs are readily activated under mild conditions, others must be heated to the point where decomposition can compete with activation. This latter class includes MOFs where the coordination of the metals to solvent must be disrupted for full activation. Here, the details of the solvent removal process are elucidated for two isostructural MOFs comprising divalent metals linked with 2,5-dioxidoterephthalate: Mg-MOF-74 and Zn-MOF-74. Using computational and spectroscopic data, structural and electronic changes undergone by the MOF are elucidated, providing insight into discrete intermediate states during the solvent removal process. Additionally, powder x-ray diffraction is analyzed to reveal features that are indicative of successful activation. These results provide a basis to design more efficient and effective MOF activation procedures.