Abstract
We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal–organic frameworks at natural abundance by 1H‐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 1H and 13C 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.
Highlights
We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal–organic frameworks at natural abundance by 1H-detected solid-state nuclear magnetic resonance (NMR)
We show that with the help of very fast (60 kHz) magic-angle spinning (MAS) rates and a set of tailored radiofrequency (RF) irradiation schemes,[46,47,48,49] paramagnetic effects can become an asset for the rapid characterisation of powdered samples of open-shell metal–organic frameworks (MOFs) at natural abundance by 1H-detected solidstate NMR
Order parameters Sord of 0.7 and 0.25, respectively, are obtained for the two spin pairs. The former corresponds to a highly restricted motion of the rigid NDC ligand,[55,56] while the latter reports on very fast internal dynamics associated with the DABCO rotation around its NÀN axis, in agreement with previous IR results,[51] as well as with 2H MAS NMR and 1H T1 relaxation studies on analogous diamagnetic materials.[57,58]
Summary
We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal–organic frameworks at natural abundance by 1H-detected solid-state NMR.
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