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Main Title: Giant spin-orbit effects on H-1 and C-13 NMR shifts for uranium(VI) complexes revisited: role of the exchange-correlation response kernel, bonding analyses, and new predictions
Author(s): Greif, Anja H.
Hrobárik, Peter
Autschbach, Jochen
Kaupp, Martin
Type: Article
Language Code: en
Abstract: Previous relativistic quantum-chemical predictions of unusually large H-1 and C-13 NMR chemical shifts for ligand atoms directly bonded to a diamagnetic uranium(VI) center (P. Hrobarik, V. Hrobarikova, A. H. Greif and M. Kaupp, Angew. Chem., Int. Ed., 2012, 51, 10884) have been revisited by two- and four-component relativistic density functional methods. In particular, the effect of the exchange-correlation response kernel, which had been missing in the previously used two-component version of the Amsterdam Density Functional program, has been examined. Kernel contributions are large for cases with large spin-orbit (SO) contributions to the NMR shifts and may amount to up to similar to 30% of the total shifts, which means more than a 50 ppm difference for the metal-bonded carbon shifts in some extreme cases. Previous calculations with a PBE-40HF functional had provided overall reasonable predictions, due to cancellation of errors between the missing kernel contributions and the enhanced exact-exchange (EXX) admixture of 40%. In the presence of an exchange-correlation kernel, functionals with lower EXX admixtures give already good agreement with experiments, and the PBE0 functional provides reasonable predictive quality. Most importantly, the revised approach still predicts unprecedented giant H-1 NMR shifts between +30 ppm and more than +200 ppm for uranium(VI) hydride species. We also predict uranium-bonded C-13 NMR shifts for some synthetically known organometallic U(VI) complexes, for which no corresponding signals have been detected to date. In several cases, the experimental lack of these signals may be attributed to unexpected spectral regions in which some of the C-13 NMR shifts can appear, sometimes beyond the usual measurement area. An extremely large uranium-bonded C-13 shift above 550 ppm, near the upper end of the diamagnetic C-13 shift range, is predicted for a known pincer carbene complex. Bonding analyses allow in particular the magnitude of the SO shifts, and of their dependence on the functional, on the ligand position in the complex, and on the overall electronic structure to be better appreciated, and improved confidence ranges for predicted shifts have been obtained.
Issue Date: 2016
Date Available: 24-Oct-2017
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Journal Title: Physical chemistry, chemical physics
Publisher: Royal Society of Chemistry
Publisher Place: Cambridge
Volume: 18
Issue: 44
Publisher DOI: 10.1039/c6cp06129j
Page Start: 30462
Page End: 30474
EISSN: 1463-9084
ISSN: 1463-9076
Notes: Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
Appears in Collections:FG Theoretische Chemie » Publications

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