Lubomír Rulíšek Group
CS

Relativistic Heavy-Neighbor-Atom Effects on NMR Shifts

The spin-orbit heavy atom on light atom effect (SO-HALA) effect arises from the relativistic spin-orbit (SO) interaction at the heavy atom, resulting in non-intuitive chemical shifts at neighboring light atoms. The effect can be either shielding or deshielding, and can greatly vary in magnitude. Our pioneering work with J. Vícha (CPM Zlín), S. Komorovsky (SAS Bratislava), and R. Marek (MU Brno) has provided the first completely general explanation how the SO-HALA effect relates to electronic structure of the HA and how the SO-HALA effect develops for HA across the Periodic Table (Vícha, 2018).

SO-HALA effect throughout the periodic table

We have established the rule, that HA induces additional relativistic shielding at neighbouring light atoms in case it has one or more electron lone pair(s) (LP), for example in the d8 Pt(II) and p4 At(I) complexes. A deshielding is then induced at LA, when HA has no occupied LP, such as the d0 Ba(II), d0f0 Ce(IV), or p0 Tl(I) complexes. The knowledge on the SO-HALA effect was summarized in a collaborative review (Vícha, 2020). These simple rules are important in understanding NMR chemical shifts in heavy atom compounds.

Recently, we have shown theoretically and experimentally, in collaboration with M. Dračínský at IOCB Prague that the SO-HALA effect can also propagate through hydrogen bonds (Vícha, 2020). This is experimentally reflected in a more shielding 1H signal in compounds with N–H...I interactions as compared to H...Br and H...Cl analogues. Theoretical analysis reveals that these differences closely correspond to the SO-HALA effect induced by iodine on the interacting H atom. This is important for understanding of NMR chemical shifts in solid state compounds.