DFT Study of the NMR Properties of Xenon in Covalent Compounds and van der Waals Complexes. Implications for the Use of 129Xe as Molecular Probe

The NMR properties (chemical shift and spin-spin coupling constants)of 129Xe in covalent compounds and weakly bound complexes have been investigated by DFT methods including relativistic effects. For covalent species, a good agreement between experimental and calculated results is achieved without scalar relativistic effects, but their inclusion (with a triple-theta, double-polarization basis set) leads to some improvement in the quality of the correlation. The spin-orbit coupling term has a significant effect on the shielding constant, but makes a small contribution to the chemical shift. Coupling constants contain substantial contributions from the Fermi contact and paramagnetic spin-orbit terms; unlike light nuclei the spin-dipole term is also large, whereas the diamagnetic spin-orbit term is negligible. For van der Waals dimers, the dependence of the xenon chemical shift and anisotropy is calculated as a function of the distance. Small (< 1 Hz) but non-negligible through-space coupling constants between 129Xe and 13C or 1H are predicted. Much larger couplings, of the order of few Hz, are calculated between xenon and 17O in a model silicate residue.