Solvent-derived defects suppress adsorption in MOF-74

Y Fu and YF Yao and AC Forse and JH Li and K Mochizuki and JR Long and JA Reimer and G De Paëpe and XQ Kong, NATURE COMMUNICATIONS, 14, 2386 (2023).

DOI: 10.1038/s41467-023-38155-8

Defects in metal-organic frameworks (MOFs) have great impact on their nano-scale structure and physiochemical properties. However, isolated defects are easily concealed when the frameworks are interrogated by typical characterization methods. In this work, we unveil the presence of solvent-derived formate defects in MOF-74, an important class of MOFs with open metal sites. With multi-dimensional solid-state nuclear magnetic resonance (NMR) investigations, we uncover the ligand substitution role of formate and its chemical origin from decomposed N,N-dimethylformamide (DMF) solvent. The placement and coordination structure of formate defects are determined by C-13 NMR and density functional theory (DFT) calculations. The extra metal-oxygen bonds with formates partially eliminate open metal sites and lead to a quantitative decrease of N-2 and CO2 adsorption with respect to the defect concentration. In-situ NMR analysis and molecular simulations of CO2 dynamics elaborate the adsorption mechanisms in defective MOF-74. Our study establishes comprehensive strategies to search, elucidate and manipulate defects in MOFs. Defects in metal-organic frameworks impact their structure and properties. Here authors uncover formate defects in MOF-74 that originate from decomposed DMF solvent. NMR shows that the defects partially eliminate open metal sites and lead to a decrease of gas adsorption; the adsorption mechanism of CO2 in defective MOF is also elucidated.

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