Toward an absolute NMR shielding scale using the spin-rotation tensor within a relativistic framework

AUCAR, IGNACIO AGUSTÍN; GOMEZ, SERGIO SANTIAGO; GIRIBET, CLAUDIA GLORIA; AUCAR, GUSTAVO ADOLFO

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 18 p. 23572 - 23586

1463-9076

One of the most influencing articles showing the best way to get absolute values of NMR magnetic shieldings, $sigma$ (non measurables) from both, accurate measurements and theoretical calculations, was published long time ago by Flygare. His model was shown to break down when heavy atoms are involved. This fact motivated the development of new theories of nuclear spin-rotation (SR) tensors, that consider electronic relativistic effects. One was published recently by some of us. In this article we do another step further and propose three different models that generalize Flygare´s one. All of them are written using four-component relativistic expressions, though the two-component relativistic SO-S term also appears in one. The first clues for these developments were built from the relationship among $sigma$ and the SR tensors within the two-component relativistic LRESC model. Besides, we had to introduce few other well defined assumptions: i) relativistic corrections must be included in a way to best reproduce the relationship among the (e-e) term (called ``paramagnetic´´ within the non-relativistic domain) of $sigma$ with its equivalent part of the SR tensor, ii) as happens in Flygare´s rule, the shielding of free atoms shall be included to improve accuracy. In the highest accurate model, a new term known as Spin-orbit due to spin, SO-S (in this mechanism the Spin-Zeeman Hamiltonian replace the Orbital-Zeeman Hamiltonian) is included. We show results of the application of those models to halogen containing linear molecules.