Systematic Assessment of the Structural Impact of Linker Fluorination in CeIV-Based UiO-66

Incorporating fluorine atoms into the organic linker is a widely adopted strategy to tune the properties of Metal–Organic Frameworks (MOFs). However, identifying a trend in how fluorine atoms modulate the structure of porous frameworks remains an unaddressed topic. We report a systematic investigation of how stepwise fluorination of 1,4-benzenedicarboxylic acid linkers (Fx-H2BDC) influences the structural features of the CeIV-based UiO-66 architecture. The complete series of fluorinated Fx_UiO-66(Ce) materials (where x = 0, 1, 2, 3, 4) was synthesized using acetic acid as a crystallization modulator in a mixed DMF:H2O solvent and fully characterized. 1H and 19F liquid-state NMR spectroscopy of digested samples, supported by thermogravimetric analysis, confirmed that all fluorinated derivatives are defect-free, whereas the nonfluorinated analogue contains a small amount of missing-linker defects. N2 adsorption measurements revealed a decreasing trend in BET surface areas with increasing fluorination. Rietveld refinements of high-resolution synchrotron powder X-ray diffraction data indicate a gradual expansion of the unit cell as the degree of fluorination increased, along with the elongation of the CeIV–Ocarboxylate bonds, while the aromatic rings are progressively twisted out of the plane of the carboxylates and a water molecule is incorporated into the coordination sphere of CeIV.