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Issue 22, 2019
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ELDOR-detected NMR beyond hyperfine couplings: a case study with Cu(ii)-porphyrin dimers

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Abstract

The pulse EPR method ELDOR-detected NMR (EDNMR) is applied to two Cu(II)-porphyrin dimers that are suitable building blocks for molecular wires. One of the dimers is mesomeso singly linked, the other one is β, meso, β-fused. We show experimentally and theoretically that EDNMR spectra contain information about the electron–electron couplings. The spectra of the singly linked dimer are consistent with a perpendicular arrangement of the porphyrin planes and negligible exchange coupling. In addition, the resolution is good enough to distinguish 63Cu and 65Cu in frozen glassy solution and to resolve a metal-ion nuclear quadrupole coupling of 32 MHz. In the case of the fused dimer, we observe so far unreported signal enhancements, or anti-holes, in the EDNMR spectra. These are readily explained in a generalized framework based on [Cox et al., J. Magn. Reson., 2017, 280, 63–78], if an effective spin of S = 1 is assumed, in accordance with SQUID measurements. The positions of the anti-holes encode a zero-field splitting with |D| = 240 MHz, which is about twice as large as expected from the point-dipole approximation. These findings demonstrate the previously unrecognized applicability and versatility of the EDNMR technique in the quantitative study of complex paramagnetic compounds.

Graphical abstract: ELDOR-detected NMR beyond hyperfine couplings: a case study with Cu(ii)-porphyrin dimers

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Publication details

The article was received on 29 Mar 2019, accepted on 21 May 2019 and first published on 21 May 2019


Article type: Paper
DOI: 10.1039/C9CP01760G
Phys. Chem. Chem. Phys., 2019,21, 11676-11688
  • Open access: Creative Commons BY-NC license
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    ELDOR-detected NMR beyond hyperfine couplings: a case study with Cu(II)-porphyrin dimers

    N. Wili, S. Richert, B. Limburg, S. J. Clarke, H. L. Anderson, C. R. Timmel and G. Jeschke, Phys. Chem. Chem. Phys., 2019, 21, 11676
    DOI: 10.1039/C9CP01760G

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