Linker Contribution toward Stability of Metal–Organic Frameworks under Ionizing Radiation

The effects of radiation on a series of UiO derivative metal–organic frameworks (MOFs) that contain the same zirconium hexamer node and similar organic linkers, UiO-66, UiO-66–NH₂, UiO-66–OH, and NU-403, were examined using γ-rays and 5 MeV He ions. UiO-66, UiO-66–NH₂, and UiO-66–OH contain aromatic linkers and are significantly more stable to radiation than NU-403. Of these, UiO-66 is the most radiation resistant, displaying crystalline features up to 47 MGy of He-ion irradiation. MOFs containing aromatic linkers functionalized by electron-donating groups, UiO-66–NH₂ and UiO-66–OH, retained crystalline features up to 19 MGy. NU-403 contains aliphatic rings and is the least radiation-resistant MOF studied here. NU-403 exhibits small changes in infrared spectra upon 3 MGy of γ-irradiation and significant damage upon 10 MGy of He-ion irradiation. Diffraction data revealed radiation-induced defect formation. Structural locations of radiation-induced breakdown were interrogated experimentally and via density functional theory. The results indicated changes in the carboxylate (−OCO) of the linker and μ₃-OH vibrational modes, suggesting that introduction of an aliphatic linker into the MOF renders the connection between the linker and metal node most susceptible to radiation damage. This study reveals that the choice of the linker is crucial in designing a radiation-resistant MOF.