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Nano Lett. 2019 Mar 13;19(3):1618-1624. doi: 10.1021/acs.nanolett.8b04518. Epub 2019 Feb 8.

Duet of Acetate and Water at the Defects of Metal-Organic Frameworks.

Fu Y1,2, Kang Z3,4, Yin J1, Cao W1, Tu Y4, Wang Q3, Kong X1.

Author information

1
Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry , Zhejiang University , Hangzhou 310027 , People's Republic of China.
2
Department of Chemical and Biomolecular Engineering , University of California , Berkeley , California 94720 , United States.
3
Department of Chemistry , Zhejiang University , Hangzhou 310027 , People's Republic of China.
4
Department of Theoretical Chemistry and Biology , KTH Royal Institute of Technology , Stockholm SE-10691 , Sweden.

Abstract

Metal-organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.

KEYWORDS:

Metal−organic frameworks; defects; dynamics; molecular dynamics simulations; solid-state NMR

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