Relativistic and Electron-Correlation Effects on the Nuclear Magnetic Resonance Shieldings of Molecules Containing Tin and Lead Atoms

Abstract

The reference values for NMR magnetic shieldings, σ ref , are of highest importance when theoretical analysis of chemical shifts are envisaged. The fact that the non relativistically valid relationship among spin-rotation constants and magnetic shieldings is not any longer valid for heavy atoms makes that the search for σ ref for such atoms needs new strategies to follow.We present here results of σ ref that were obtained applying an own simple procedure which mix accurate experimental chemical shifts (δ) and theoretical magnetic shieldings (σ). We calculated σ(Sn) and σ(Pb) in a family of heavy-halogen containing molecules.We found out that σ ref (Sn; Sn(CH 3 ) 4 ) in gas phase should be close to 3864.11 ± We studied tin and lead shieldings of the XY 4−n Z n (X = Sn, Pb; Y , Z = H, F, Cl, Br, I) and PbH 4−n I n (n = 0, 1, 2, 3, 4) family of compounds with four-component functionals as implemented in the DIRAC code. For these systems results of calculations with RelPPA-RPA are more reliable than the DFT ones. We argue on why those DFT functionals must be modified in order to obtain more accurate results of NMR magnetic shieldings within the relativistic regime: first, there is a dependence among both, electron correlation and relativistic effects that should be introduced in some way in the functionals; and second, the DIRAC code uses standard non-relativistic functionals and the functionals B3LYP and PBE0 were parameterized only with data taken from light elements. It can explain why they are not able to properly introduce relativistic effects on nuclear magnetic shieldings.We finally show that in the analysis of magnetic shieldings for the family of compounds mentioned above, one must consider the newest and so called heavy-atom effect on vicinal heavy atoms, HAVHA. Such effects are among the most important relativistic effects in these kind of compounds.

Relativistic corrections to the electric field gradient given by linear response elimination of the small component formalism

“…For Hg X 2 molecules, all corrections have almost the same value when the weight of the halogen grows up, meaning that no heavy atom on vicinal heavy atom effect happens . This fact tells that LRESC corrections mostly depend on the weight of the central mercury atom, showing a “core‐nature” for this kind of molecular systems.…”

Spin–orbit effects on the 119Sn magnetic-shielding tensor in solids: a ZORA/DFT investigation

“…[38][39][40] For example, Malkin et al 41 recently proposed that the 119 Sn magnetic-shielding scale should be increased by around 1000 ppm, a result obtained from the four-component (4c) relativistic theory. [38][39][40] For example, Malkin et al 41 recently proposed that the 119 Sn magnetic-shielding scale should be increased by around 1000 ppm, a result obtained from the four-component (4c) relativistic theory.…”

Theoretical developments and applications of polarization propagators

“…They were studied since 30 years ago for many research groups in a vast variety of molecular systems. However, few years ago a third heavy atom effect was proposed in our research group, termed the HAVHA (heavy‐atom effects on vicinal‐heavy‐atoms) effect . New studies were then needed to find enough evidence for this effect.…”

“…However, few years ago a third heavy atom effect was proposed in our research group, termed the HAVHA (heavy-atom effects on vicinal-heavy-atoms) effect. [105][106][107][108] New studies were then needed to find enough evidence for this effect. Thus, even though there are many studies on the NMR spectroscopic parameters for heavy-atom containing molecules, the HAVHA effect was not included in any of their analyses.…”