Analyzing Pt chemical shifts calculated from relativistic density functional theory using localized orbitals: The role of Pt 5d lone pairs

Abstract

Pt chemical shifts were calculated from two-component relativistic density functional theory (DFT). The shielding tensors were analyzed by using a recently developed method to decompose the spin-orbit DFT results into contributions from spin-free localized orbitals (here: natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs)). Seven chemical shifts in six Pt complexes with Pt oxidation states II, III, and IV; and halide, amino, and amidate ligands were analyzed, with particular focus on the role of nonbonding Pt 5d orbitals. A simple d-orbital 'rotation' model has been used to rationalize some of the observed trends such as the main difference between Pt(II) and Pt(IV) chemical shifts. The localized orbital analysis data showed that most of this difference as well as trends among different Pt complexes with similar coordination can be rationalized by comparing properties of the nonbonding Pt 5d orbitals. We have also analyzed the spin-orbit effects on the chemical shifts of [PtCl4](2-) compared to [PtBr4](2-).

Modeling of Heavy‐Atom–Ligand NMR Spin–Spin Coupling in Solution: Molecular Dynamics Study and Natural Bond Orbital Analysis of HgC Coupling Constants

“…With this we demonstrate that at an ab initio MD level with explicit solvation one obtains a similar increase in JA C H T U N G T R E N N U N G (Hg À C) as previously predicted from static DFT calculations. The other purpose is to use relativistic natural bond orbital and natural localized molecular orbital (NBO/NLMO) techniques for J coupling decompositions [30,31] to analyze the solvent effects in detail. Due to the computational expense of the MD simulations and the amount of detail generated by the analysis we focus on two of the systems studied previously in reference [6] that exhibit particularly pronounced increases in JA C H T U N G T R E N N U N G (Hg À C).…”

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

“…At the same time, the orbital energies for the parent NBOs of the La-X bonding NLMOs slightly increase along the F-I series (LaF 3 : −0.374, LaCl 3 : −0.369, LaBr 3 : −0.353, LaI 3 : −0.336 au), as already mentioned in the MO analysis section. As argued elsewhere, [30] smaller occupied-unoccupied orbital gaps also translate into overall larger shielding terms from localized, not just canonical, orbitals if all other factors remain equal. Therefore, the increase of the magnitude of the paramagnetic terms seen in the La-X bonding NLMOs can be attributed to (i) increasing orbital charge density centered at at La, and (ii) slightly decreasing orbital gaps between occupied NLMOs and unoccupied orbitals.…”

“…[36] Nuclear shielding tensors were calculated with the 'NMR' code [37,38] and NLMOs and NBOs were generated, at the scalar relativistic level, using the NBO 5.0 program by Weinhold et al [39] Orbital visualizations were prepared with the 'adfview' tool of the ADF graphical user interface. For details about the implementation of the localized orbital-based NMR shielding analysis see Refs [29][30][31]. New tests performed as part of this work suggest that the analysis is somewhat origin dependent for individual NLMO contributions, but their sum, the total shielding, is origin independent since it is calculated with gauge-including basis functions (GIAOs).…”

“…ZORA) analogs of the paramagnetic (OP), Fermi-contact and spin-dipole (FC, SD), orbital Zeeman (OZ), spin-Zeeman (SZ), and the diamagnetic shielding (DS) operators and their two-electron analogs. [30] In the sumover-states (SOS) part of the equation, the usual paramagnetic shielding term is a result of the OP-OZ operator combination, while the SO terms result from the remaining combinations, OP-SZ and (FC+SD) − (OZ+SZ). However, there are also SO effects in the electronic structure [ 0 , j in Eqn (1), or the electron density in density functional theory (DFT)], meaning there are also SO effects on the diamagnetic term, and on the paramagnetic OP-OZ mechanism.…”

“…New relativistic molecular orbital (MO) based analysis tools have been developed recently in our group for the interpretation of heavy-atom chemical shift trends [29,30] and J-coupling, [31] but they have not yet been widely applied. So-called natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs) [32] generated for a scalar (spin-free) relativistic reference electronic structure are employed in these types of calculations.…”