Insights into trans-Ligand and Spin-Orbit Effects on Electronic Structure and Ligand NMR Shifts in Transition-Metal Complexes.
Surprisingly general effects of trans ligands L on the ligand NMR shifts in third-row transition-metal complexes have been found by quasi-relativistic computations, encompassing 5d10, 5d8, and to some extent even 5d6situations. Closer analysis, with emphasis on1H shieldings in a series of linear HAuILqcomplexes, reveals a dominance of spin-orbit (SO) effects, which can change sign from appreciably shielding for weak trans ligands to appreciably deshielding for ligands with strong trans influence. This may be traced back to increasing destabilization of a σ-type MO at scalar relativistic level, which translates into very different σ-/π-mixing if SO coupling is included. For the strongest trans ligands, the σ-MO may move above the highest occupied π-type MOs, thereby dramatically reducing strongly shielding contributions from predominantly π-type spinors. The effects of SO-mixing are in turn related to angular momentum admixture from atomic spinors at the metal center. These SO-induced trends hold for other nuclei and may also be used to qualitatively predict shifts in unknown complexes.
Technische Universität Berlin, Institut für Chemie, Theoretische Chemie/Quantenchemie, Sekr. C7, Strasse des 17. Juni 135, 10623, Berlin, Germany.
Anja H
AH
Greif
Technische Universität Berlin, Institut für Chemie, Theoretische Chemie/Quantenchemie, Sekr. C7, Strasse des 17. Juni 135, 10623, Berlin, Germany.|Faculty of Natural Sciences, Comenius University, Department of Inorganic Chemistry, Mlynská dolina CH-2, 84215, Bratislava, Slovakia.
Peter
http://orcid.org/0000-0002-6444-8555
P
Hrobárik
Technische Universität Berlin, Institut für Chemie, Theoretische Chemie/Quantenchemie, Sekr. C7, Strasse des 17. Juni 135, 10623, Berlin, Germany.
Martin
http://orcid.org/0000-0003-1582-2819
M
Kaupp
NMR shifts; electronic structure; ligand effects; relativistic NMR calculations; spin-orbit effects; trans influence; transition metal hydrides