Metal-Organic Frameworks (MOFs) are a class of crystalline compounds whose scaffolding derives from metal clusters or ions that are interconnected by organic linkers. The high number of possible combinations of metals and ligands leads to high tunability of macroscopic properties and thus it is possible to employ MOFs in many fields of applications, including gas storage, gas separation, and catalysis [1,2]. In the design and development of a new MOF it is extremely important to completely understand every macroscopic property of the compound and to relate it to its microscopic origin. Many techniques can be exploited and combined to characterize the structural and dynamic properties of a MOF. Among them, Solid State Nuclear Magnetic Resonance (SSNMR) spectroscopy is certainly one of the most important because it can shed light on many aspects of the compound at a molecular level, such as 3D structure, porosity [3], local dynamics [4], and host-guest interactions [5]. In this work, 1H, 13C, and 19F SSNMR spectroscopy has been employed to characterize two MOFs belonging to the MIL140A class: F4-MIL140A(Ce) and F3-MIL140A(Ce). These MOFs share the same metal SBU composed by CeIV, but the organic linker has a different degree of fluorination. The former is based on tetrafluoroterephthalic acid (F4-BDC), the latter on trifluoroterephthalic acid (F3-BDC). F4-MIL140A(Ce) is extremely relevant in the field of gas separation and storage because it presents a step-shaped adsorption isotherm for CO2 [6]. F3-MIL140A(Ce), instead, is a novel MOF that could in principle show similar or even better adsorption properties with respect to the perfluorinated analogue. Multinuclear SSNMR experiments and 2D correlation spectra have been used to obtain, also by comparison with powder X-ray diffraction data, a detailed characterization of the framework structure both in the presence and after removal of crystallization water. Moreover, the analysis of variable-temperature 19F spin-lattice relaxation times at different magnetic fields has been applied for the investigation of the dynamic processes involving the fluorinated linkers, which are supposed to be involved in the MOF adsorption mechanism. This work was supported by MUR - PRIN 2020 grant n. 2020P9KBKZ. References [1] Q. Qian et al., Chem. Rev. 120, 8161, (2020). [2] X. L. and H. T. Jian Cao, Curr. Med. Chem. 27, 5949, (2020). [3] N. Klein et al., Phys. Chem. Chem. Phys. 12, 11778, (2010). [4] X. Kong et al., J. Am. Chem. Soc. 134, 14341 (2012). [5] A. E. Khudozhitkov et al., J. Phys. Chem. C, 120, 21704 (2016). [6] R. D'Amato et al., ACS Sustain. Chem. Eng. 7, 394-402 (2019).
STRUCTURAL PROPERTIES AND DYNAMICS OF FLUORINATED METAL-ORGANIC FRAMEWORKS BY SOLID STATE NMR
L Calucci;
2022
Abstract
Metal-Organic Frameworks (MOFs) are a class of crystalline compounds whose scaffolding derives from metal clusters or ions that are interconnected by organic linkers. The high number of possible combinations of metals and ligands leads to high tunability of macroscopic properties and thus it is possible to employ MOFs in many fields of applications, including gas storage, gas separation, and catalysis [1,2]. In the design and development of a new MOF it is extremely important to completely understand every macroscopic property of the compound and to relate it to its microscopic origin. Many techniques can be exploited and combined to characterize the structural and dynamic properties of a MOF. Among them, Solid State Nuclear Magnetic Resonance (SSNMR) spectroscopy is certainly one of the most important because it can shed light on many aspects of the compound at a molecular level, such as 3D structure, porosity [3], local dynamics [4], and host-guest interactions [5]. In this work, 1H, 13C, and 19F SSNMR spectroscopy has been employed to characterize two MOFs belonging to the MIL140A class: F4-MIL140A(Ce) and F3-MIL140A(Ce). These MOFs share the same metal SBU composed by CeIV, but the organic linker has a different degree of fluorination. The former is based on tetrafluoroterephthalic acid (F4-BDC), the latter on trifluoroterephthalic acid (F3-BDC). F4-MIL140A(Ce) is extremely relevant in the field of gas separation and storage because it presents a step-shaped adsorption isotherm for CO2 [6]. F3-MIL140A(Ce), instead, is a novel MOF that could in principle show similar or even better adsorption properties with respect to the perfluorinated analogue. Multinuclear SSNMR experiments and 2D correlation spectra have been used to obtain, also by comparison with powder X-ray diffraction data, a detailed characterization of the framework structure both in the presence and after removal of crystallization water. Moreover, the analysis of variable-temperature 19F spin-lattice relaxation times at different magnetic fields has been applied for the investigation of the dynamic processes involving the fluorinated linkers, which are supposed to be involved in the MOF adsorption mechanism. This work was supported by MUR - PRIN 2020 grant n. 2020P9KBKZ. References [1] Q. Qian et al., Chem. Rev. 120, 8161, (2020). [2] X. L. and H. T. Jian Cao, Curr. Med. Chem. 27, 5949, (2020). [3] N. Klein et al., Phys. Chem. Chem. Phys. 12, 11778, (2010). [4] X. Kong et al., J. Am. Chem. Soc. 134, 14341 (2012). [5] A. E. Khudozhitkov et al., J. Phys. Chem. C, 120, 21704 (2016). [6] R. D'Amato et al., ACS Sustain. Chem. Eng. 7, 394-402 (2019).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
