Monitoring Dynamics, Structure, and Magnetism of Switchable Metal-Organic Frameworks via H-1-Detected MAS NMR

We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal-organic frameworks at natural abundance by H-1-detected solid-state NMR. Very fast MAS rates at room and cryogenic temperatures and a set of tailored radiofrequency irradiation schemes help overcome the sensitivity and resolution limits often associated with the characterisation of MOF materials. We demonstrate the approach on DUT-8(Ni), a framework containing Ni2+ paddle-wheel units which can exist in two markedly different architectures. Resolved H-1 and C-13 resonances of organic linkers are detected and assigned in few hours with only 1-2 mg of sample at natural isotopic abundance, and used to rapidly extract information on structure and local internal dynamics of the assemblies, as well as to elucidate the metal electronic properties over an extended temperature range. The experiments disclose new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.

Automated summary

A toolbox for rapid characterization of powdered samples of paramagnetic metal-organic frameworks by H-1-detected solid-state NMR was presented, with tailored radiofrequency irradiation schemes and fast MAS rates helping to overcome sensitivity and resolution limits. The approach was demonstrated on DUT-8(Ni) to detect and assign H-1 and C-13 resonances of organic linkers in a few hours with only 1-2 mg of sample, providing information on structure, dynamics, and metal electronic properties. The experiments revealed new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.