Molecular orbital analysis of the inverse halogen dependence of nuclear magnetic shielding in LaX3, X = F, Cl, Br, I

作者：Moncho Salvador; Autschbach Jochen^*

来源：Magnetic Resonance in Chemistry, 2010, 48: S76-S85.

DOI：10.1002/mrc.2632

The NMR nuclear shielding tensors for the series LaX3, with X = F, CI, Br and I, have been computed using two-component relativistic density functional theory based on the zeroth-order regular approximation (ZORA). A detailed analysis of the inverse halogen dependence (IHD) of the La shielding was performed via decomposition of the shielding tensor elements into contributions from localized and delocalized molecular orbitals. Both spin-orbit and paramagnetic shielding terms are important, with the paramagnetic terms being dominant. Major contributions to the IHD can be attributed to the La-X bonding orbitals, as well as to trends associated with the La core and halogen lone pair orbitals, the latter being related to X-La pi donation. An 'orbital rotation' model for the in-plane pi acceptor f orbital of La helps to rationalize the significant magnitude of deshielding associated with the in-plane pi donation. The IHD goes along with a large increase in the shielding tensor anisotropy as X becomes heavier, which can be associated with trends for the covalency of the La -X bonds, with a particularly effective transfer of spin-orbit coupling induced spin density from iodine to La in Lal(3).

• 出版日期2010-12