An investigation of lanthanum coordination compounds by using solid-state La-139 NMR spectroscopy and relativistic density functional theory

Lanthanum-139 NMR spectra of stationary samples of several solid La-III coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T The breadth and shape of the La-139 NMR spectra of the central transition are dominated by the interaction between the La-139 nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical-shift anisotropy on the NMR spectra is non-negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the La-139 quadrupolar coupling constants (C-Q) range from 10.0 to 35.6 MHz, the spans of the chemical-shift tensor (Omega) range from 50 to 260 ppm, and the isotropic chemical shifts (delta(iso)) range from -80 to 178 ppm. In general, there is a correlation between the magnitudes of C-Q and Omega, and delta(iso) is shown to depend on the La coordination number. Magnetic-shielding tensors, calculated by using relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) and incorporating scalar only or scalar plus spin-orbit relativistic effects, qualitatively reproduce the experimental chemical-shift tensors. In general, the inclusion of spin-orbit coupling yields results that are in better agreement with those from the experiment. The magnetic-shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical-shift and EFG tensors in the molecular frame. This study demonstrates that solid-state La-139 NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.