Transmission of spin-polarization by π-orbitals : an approach to assessing its effect on NMR spin-spin coupling and EPR hyperfine structure
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A new approach to assessing the effect of the transmission of spin-polarization by π-orbitals (π-TSP) is presented. In order to switch off the π-TSP effect, we artificially average the α- and β-densities of the valence π-orbitals when calculating the exchange–correlation contribution to the Fock matrix in the unrestricted Kohn–Sham framework. The π-TSP effect is then evaluated as the difference between the results obtained with switched-on and switched-off options. This approach is applied to estimate the π-TSP effect on the Fermi-contact contribution to spin–spin couplings and EPR hyperfine structure coupling constants. The π-TSP effect on the distribution of spin-density, spin–spin coupling pathways and pathways of EPR hyperfine couplings is demonstrated for benzene, naphthalene, 1,3,5,7,9-decapentaene and the 1,3,5,7,9-decapentaen-1-yl radical. The sign alternation of the spin-polarization transmitted by π-orbitals is explained in a theoretical framework based on perturbation theory. However, the delocalized nature of the π-system can interfere with the sign alternation in certain cases, two of which – the cyclobutadiene dication and the cyclooctatetraene dication – are examined, and an explanation for which is provided.
Malkina , O L , Lemken , F , Asher , J R , Hierso , J-C , Buehl , M & Malkin , V G 2022 , ' Transmission of spin-polarization by π-orbitals : an approach to assessing its effect on NMR spin-spin coupling and EPR hyperfine structure ' , Physical Chemistry Chemical Physics , vol. Advance Article . https://doi.org/10.1039/D2CP03295C
Physical Chemistry Chemical Physics
Copyright © 2022 The Author(s). This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1039/D2CP03295C
DescriptionFunding: We acknowledge the support from Slovak-French PHC Stefanik project “Spin Coupling Advanced Level Perception” (SCALP). OM, VM and JRA acknowledge the support from Slovak grant agencies APVV (grants No. SK-FR-19-0001 and APVV-19-0516) and VEGA (grant No. 2/0135/21). This work was also supported by the CNRS, the Université de Bourgogne, the Conseil Régional BFC (CHIMENE project), the PIA-excellence ISITE-BFC program (COMICS project) and the FEDER, which are all sincerely thanked.
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