The importance of relativistic effects for carbon as an NMR reporter nucleus in carbide bridged [RuCPt]-complexes

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Carbide-bridged ruthenium platinum complexes of the general formula trans-(Cy3P)2Cl2Ru≡C-PtCl2-L show a remarkable ability to probe the ligand donor strength of the ligand L. An experimentally observed linear correlation between carbide chemical shifts (shielding) and the platinum-carbide (Pt-C) coupling constants in the complexes is investigated computationally to understand the origin of this trend. The shielding and coupling constants are computed at the two-component/spin-orbit ZORA-DFT level. The calculated values are in good agreement with the experimental values and reproduce the observed linear variation, even though relativistic effects are large and significant, especially for the Pt-C coupling constants. Analysis of the contributions to the shielding constants indicates that σ(C) is relatively more influenced by relativistic effects than σ(Ru). The variation in σ(C) originates from the spin-orbit coupling contribution, whereas the Fermi contact term is responsible for the changes in J(Pt-C) as the trans-influence of L changes. The linear correlation between parameters is therefore an illustration of the similarity of the mechanism underlying both contributions. The results are further analyzed by decomposition into contributions from natural localized molecular orbitals (NLMOs). The character of the individual NLMOs changes little along the series of complexes, and the variation in σ(C) is to equal amounts due to contributions from NLMOs associated with the Ru≡C and with the Pt-C bonds. The variation in the Pt-C coupling, on the other hand, is mainly due to variation in the contributions from NLMOs associated with only the Pt-C bond.
Original languageEnglish
Issue number10
Pages (from-to)1443-1453
Publication statusPublished - 24 May 2021

    Research areas

  • Faculty of Science - NMR, chemical shift, Spin-spin coupling constant, Chemical shielding, trans-effect, Carbide-complexes, ruthenium, platinum, relativistic effects, spin-orbit coupling, Density functional theory, ZORA

ID: 260603572