Rapid Acquisition of Rh Solid-State NMR Spectra by P Detection and Sideband Selective Methods.

Rh solid-state nuclear magnetic resonance (SSNMR) spectroscopy is potentially a powerful method for investigating the molecular and electronic structure of rhodium compounds. However, Rh is a difficult nucleus to study by NMR spectroscopy because of its small gyromagnetic ratio, broad chemical shift range, and long spin-lattice relaxation times (). While there are many prior reports demonstrating acquisition of Rh solution NMR spectra, there are few examples of Rh SSNMR spectra in the literature. Here, we utilize the large P-Rh scalar couplings (-couplings) to efficiently acquire P-detected high-resolution Rh SSNMR spectra. P{Rh} -resolved NMR experiments were used to measure P-Rh -couplings. Sideband selective SSNMR techniques originally developed for wide-line Pt SSNMR experiments were then used to rapidly acquire Rh SSNMR spectra. Notably, we were able to acquire MAS Rh SSNMR spectra in experiment times on the order of 30 min to a few hours and from only a few mg of materials. The sideband selective experiments offer significant time savings as compared to existing direct detection methods, which require days of acquisition to obtain a directly detected MAS spectrum, or yield low-resolution static powder patterns. Numerical fits of the SSNMR spectra provide Rh chemical shift tensor parameters, with the experimental spectra agreeing well with the DFT-calculated spectra.