Guests Like Gear Levers: Donor Binding to Coordinatively Unsaturated Metal Sites in MIL-101 Controls the Linker′s Rotation |
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Authors: | Alexander E Khudozhitkov Dr Sergey S Arzumanov Dr Daniil I Kolokolov Prof Oxana A Kholdeeva Prof Dieter Freude Prof Alexander G Stepanov |
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Institution: | 1. Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of, Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk, 630090 Russia;2. Faculty for Physics and Earth Sciences, Leipzig University, Linnéstr. 5, 04103 Leipzig, Germany |
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Abstract: | We present investigation of the effect of electron-donor guests on framework mobility in the metal–organic framework (MOF) MIL-101(Cr) monitored by solid state 2H NMR spectroscopy. In a guest-free material, the mobile phenylene fragments of the terephthalate (TP) linkers populate two fractions with notably different kinetic parameters for torsional motion. Two fractions of rotational motion are indicative of non-equivalence of TP linker binding to the Cr3O trimer, the primary building unit of the MIL-101 framework. It is established that the interaction of the guest molecules with coordinatively unsaturated metal sites (CUS) of the MOF dramatically decreases torsional barriers for the linker motions, enhancing the rotation rate. This result is opposite to a more conventional slowing down effect on the linker rotation of the guests not selectively interacting with the adsorption sites inside the framework of the MOFs. The effect of coordination on both the torsional barrier and the rotation rate depends notably on the particular guest interacting with the CUS. The found effects of the guest on the rotational motion represent a basis for developing the strategy for ruling and controlling the linker rotation in MOFs with CUS. It is shown that if water occupies CUS, another guest (tert-butanol, cyclohexanone) fails to competitively coordinate to the site. |
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Keywords: | materials science metal–organic frameworks rotation control solid state NMR spectroscopy structural mobility |
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