Relativistic effects on magnetic shieldings

A. F. MALDONADO; G. A. AUCAR; J. I. MELO

Smolenice

Conferencia; Eleventh International Conference on Relativistic Effects In Heavy-Elements (REHE) 2014; 2014

INSTITUTE OF INORGANIC CHEMISTRY

The reference values for NMR magnetic shieldings, sigma ref, are of highest importance when theoretical analysis of chemical shifts are envisaged. The nonrelativistically valid relationship among spin-rotation constants and magnetic shieldings is not any longer valid for heavy atoms. We present results of sigma ref that were obtained applying an own simple procedure which mix accurate experimental chemical shifts (delta) and theoretical magnetic shieldings (sigma). We calculated sigma(Sn) in a family of heavy-halogen containing molecules and we found out that sigma ref [Sn; Sn(CH3)4] in gas phase should be close to 3864.11 ppm ±20.05 ppm (0.5 %). Such theoretical value correspond to calculations with the relativistic polarization propagator method, RelPPA, at RPA level of approach. They are closer to experimental values as compared to those obtained applying few different functionals of the density functional theory, DFT. The nuclear magnetic shieldings of Sn in SnH4-nYn molecular systems (Y = F, Cl, Br, I; n = 1 - 4) are highly influenced by the substitution of one or more hydrogen by halogen heavy atoms. We applied the linear response elimination of small components (LRESC) formalism to calculate those shieldings and learn whether including only few of the leading relativistic correcting terms is sufficient to be able to quantitatively reproduce the full relativistic value. We also analyzed each relativistic correction afforded by the LRESC method and split them in two: core-dependent and ligand-dependent contributions; we then looked for the electronic mechanisms involved in the different relativistic effects and in the total relativistic value.