Investigation of Magnetic Shielding in Xenon Difluoride Using Solid-State NMR Spectroscopy and Relativistic Density Functional Theory

The xenon and fluorine magnetic shielding tensors, σ, of XeF 2 are characterized using solid-state 129 Xe and 19 F NMR spectroscopy and nonrelativistic and spin−orbit relativistic zeroth-order regular approximation density functional theory (ZORA DFT). Analysis of 129 Xe and 19 F NMR spectra acquired with magic-angle spinning at several spinning rates indicates that the Xe and F magnetic shielding tensors are axially symmetric, as dictated by the crystal symmetry. The isotropic 129 Xe chemical shift is −1603 ± 5 ppm with respect to OXeF 4 (neat liquid, 24 °C) and the Xe magnetic shielding anisotropy, Ω, is 4245 ± 20 ppm, the first anisotropy measured directly for a xenon compound. The parallel component of the experimentally determined xenon chemical shift tensor, δ ∥ = −4433 ppm differs from δ(Xe(free atom)) by ∼1000 ppm, providing the first experimental demonstration that relativistic effects play an important role in the nuclear magnetic shielding for xenon. Both the sign and magnitude of the isotropic indirect 129 Xe, 19 F nuclear spin−spin coupling constant are determined, −5560 ± 50 Hz. Analysis of the 19 F NMR spectra yield Ω(F) = 150 ± 20 ppm. The ZORA DFT method has been employed to calculate σ(Xe) and σ(F) for isolated XeF 2 and XeF 4 molecules, as well as σ(Kr) and σ(F) for an isolated KrF 2 molecule, at the relativistic and nonrelativistic levels of theory. Spin−orbit relativistic DFT results for Ω(Xe) are in very good agreement with those determined experimentally and highlight the importance of relativistic effects.