Ultrafast Rotation In An Amphidynamic Crystalline Metal Organic Framework

Keywords

Amphidynamic crystals; Metal-organic frameworks; Molecular machines; Molecular rotors; Smart materials

Abstract

Amphidynamic crystals are an emergent class of condensed phase matter designed with a combination of lattice-forming elements linked to components that display engineered dynamics in the solid state. Here, we address the design of a crystalline array of molecular rotors with inertial diffusional rotation at the nanoscale, characterized by the absence of steric or electronic barriers. We solved this challenge with 1,4-bicyclo[2.2.2]octane dicarboxylic acid (BODCA)-MOF, a metal-organic framework (MOF) built with a high-symmetry bicyclo[2.2.2]octane dicarboxylate linker in a Zn4O cubic lattice. Using spin-lattice relaxation 1H solid-state NMR at 29.49 and 13.87 MHz in the temperature range of 2.3-80 K, we showed that internal rotation occurs in a potential with energy barriers of 0.185 kcal mol-1. These results were confirmed with 2H solid-state NMR line-shape analysis and spin-lattice relaxation at 76.78 MHz obtained between 6 and 298 K, which, combined with molecular dynamics simulations, indicate that inertial diffusional rotation is characterized by a broad range of angular displacements with no residence time at any given site. The ambient temperature rotation of the bicyclo[2.2.2]octane (BCO) group in BODCA-MOF constitutes an example where engineered rotational dynamics in the solid state are as fast as they would be in a high-density gas or in a low-density liquid phase.

Publication Date

12-26-2017

Publication Title

Proceedings of the National Academy of Sciences of the United States of America

Volume

114

Issue

52

Number of Pages

13613-13618

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1073/pnas.1708817115

Socpus ID

85039756797 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85039756797

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