Vibrational spectroscopy investigation of defects in Zr- and Hf-UiO-66

• Published in: RSC advances 2022-08, Vol.12 (35), p.2244-22447
• Main Authors: Yost, Brandon T, Gibbons, Bradley, Wilson, Addison, Morris, Amanda J, McNeil, L. E
• Format: Article
• Language: English
• Subjects: Chemistry; Clusters; Crystal defects; Crystal structure; Doppler effect; Gas sensors; Infrared absorption; Infrared spectroscopy; Metal-organic frameworks; Red shift; Spectrum analysis; Topology; Vibration mode; X ray powder diffraction
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d2ra03131k

Defect engineering in metalorganic framework compounds has allowed for improvements in catalysis-based functionalities, gas sensing, and gas storage. Metalorganic framework UiO-66 compounds with Zr- and Hf-based metal secondary building units were studied with Raman and infrared vibrational spectroscopy. Missing linker and missing cluster defects were engineered into the crystal structure via a modulated synthesis technique. Missing cluster defects in Hf-UiO-66 are first characterized by powder X-ray diffraction (PXRD) whereby two low-angle peaks were fit to extract the relative quantity of reo topology in four defective samples. A monotonic red-shift of the Raman-active HfO coordination bond vibration is interpreted as a signature of missing cluster defects, resulting from less-rigid charge-balancing monocarboxylate formate ions replacing the dicarboxylate linker molecule. This signature is hypothesized to be independent of the topology in which the defects appear. Missing linker defects in Zr-UiO-66 are characterized by infrared absorption spectroscopy by the quenching of CC and CH vibrational modes confined to the linker molecule. Together, Raman and infrared vibrational spectroscopies coupled with standard characterization techniques are employed to directly probe the nature of defects as well as offer new characterization tools for missing cluster defects in UiO-66. Missing cluster defects in Hf-UiO-66 cause a redshift of a distinct peak in the Raman spectrum.