Structure and bonding in rhodium coordination compounds: a ¹⁰³Rh solid-state NMR and relativistic DFT study

This study demonstrates the application of ¹⁰³Rh solid-state NMR (SSNMR) spectroscopy to inorganic and organometallic coordination compounds, in combination with relativistic density functional theory (DFT) calculations of ¹⁰³Rh chemical shift tensors and their analysis with natural bond orbital (NBO) and natural localized molecular orbital (NLMO) protocols, to develop correlations between ¹⁰³Rh chemical shift tensors, molecular structure, and Rh-ligand bonding. ¹⁰³Rh is one of the least receptive NMR nuclides, and consequently, there are very few reports in the literature. We introduce robust ¹⁰³Rh SSNMR protocols for stationary samples, which use the broadband adiabatic inversion-cross polarization (BRAIN-CP) pulse sequence and wideband uniform-rate smooth-truncation (WURST) pulses for excitation, refocusing, and polarization transfer, and demonstrate the acquisition of ¹⁰³Rh SSNMR spectra of unprecedented signal-to-noise and uniformity. The ¹⁰³Rh chemical shift tensors determined from these spectra are complemented by NBO/NLMO analyses of contributions of individual orbitals to the ¹⁰³Rh magnetic shielding tensors to understand their relationship to structure and bonding. Finally, we discuss the potential for these experimental and theoretical protocols for investigating a wide range of materials containing the platinum group elements.