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

Abstract

The NMR nuclear shielding tensors for the series LaX(3), with X = F, Cl, 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 π donation. An 'orbital rotation' model for the in-plane π acceptor f orbital of La helps to rationalize the significant magnitude of deshielding associated with the in-plane π 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 LaI(3).

DFT calculations of 29Si-NMR chemical shifts in Ru(ii) silyl complexes: Searching for trends and accurate values

“…The influence of the core and valence electrons was also reported by Autschbach for a series of LaX 3 (X = F, Cl, Br and I) complexes. 49 In this case also, the core contribution was not constant.…”

Relativistic Effects in NMR of New Prospective Water-Soluble Ligands SeP(CH2OH)3 and H[Se2P(CH2OH)2]

“…The local nature of NMR shielding makes a localized orbital description often much better suited for analysis of such type of molecular property [48]. ADF package allows to decompose NMR shielding into contributions from the so-called Natural Localized Molecular Orbitals (NLMOs) [24] generated for a scalar (spin-free) relativistic reference electronic structure.…”

“…where in a two-component relativistic calculation (ZORA), the operators correspond to the two-component analogs of the Orbital Paramagnetic (OP), Fermi-Contact (FC), Spin-Dipole (SD), Orbital Zeeman (OZ), Spin-Zeeman (SZ), and the Diamagnetic Shielding (DS) operators [45][46][47][48]. Calculated shielding is usually decomposed into diamagnetic term (the result of DS operator), paramagnetic term (the result of the OP-OZ operator combination), and spin-orbit term that results from the remaining combinations: OP-SZ and (FC ?…”

Effects of stereoelectronic interactions on the relativistic spin–orbit and paramagnetic components of the 13C NMR shielding tensors of dihaloethenes

“…62,63 In any case, our results indicate that such effects may explain the higher frequency of 13 C NMR of the cis isomer for bromine and iodine derivatives. 16,62 However, the NLMOs are similar to orbitals obtained with other localization techniques and appear as a suitable option for determining the contributions of LPs. 63 The NBO shielding analysis was indeed unable to identify the steric repulsion between iodine atoms, though this behavior is not surprising.…”

“…It has been discussed in the literature 62 that NBOs may lead to different interpretations from orbitals obtained by other localization procedures. 16 In this study the delocalization interactions were essential in supporting the role of antibonding orbitals and relating them to the orbital rotation model and the paramagnetic shielding. 16,62 However, the NLMOs are similar to orbitals obtained with other localization techniques and appear as a suitable option for determining the contributions of LPs.…”