Pushing Limits of Ultra-widelineSolid-State NMR Spectroscopy:NMR Signatures of ²⁰⁹Bi and ¹²⁷I in Metal–OrganicFrameworks at Ultra-high Magnetic Fields

Bismuth- and iodine-containing metal–organic frameworks (MOFs) are crucial in catalysis, gas adsorption, and luminescence, with local environments of Bi and I ions shaping their performance. Using ²⁰⁹Bi and ¹²⁷I solid-state NMR (SSNMR) for characterization is extremely challenging due to the exceedingly large quadrupolar interactions in MOFs. Here, we present ultra-wideline (UW) SSNMR spectra of eight MOFs acquired at ultra-high magnetic fields up to 36 T, with breadths of 8–50 MHz, revealing very large quadrupolar couplings. These spectra uncover key structural details, including dehydration, guest adsorption, phase transitions, and disorder. This study establishes ²⁰⁹Bi and ¹²⁷I UW SSNMR as powerful tools for probing Bi and I ions in weight-dilute systems, offering broad applications in catalysis, solar cells, biochemistry, and beyond.