25 Mg Solid-State NMR: A Sensitive Probe of Adsorbing Guest Molecules on a Metal Center in Metal–Organic Framework CPO-27-Mg

Metal-organic frameworks (MOFs) have excellent adsorption capability. To understand their adsorptive properties requires detailed information on the host-guest interaction. The information on MOF desolvation (or activation) is also crucial because the very first step of many applications requires removal of the solvent molecules occluded inside of the pores. Unfortunately, such information is not always available from powder XRD data. Solid-state NMR is an excellent complementary technique to XRD. CPO-27-Mg is a MOF with unusual adsorption ability. The adsorption involves a direct interaction between Mg and guest species. Herein, we present, for the first time, a natural abundance (25)Mg solid-state NMR study of CPO-27-Mg at an ultrahigh magnetic field of 21.1 T. The results provide new physical insights into the effects of dehydration/rehydration and adsorption of guest species on the Mg local environment.