ELDOR-detected NMR beyond hyperfine couplings: a case study with Cu(ii)-porphyrin dimers. Issue 22 (28th May 2019)

• Record Type: Journal Article
• Authors: Wili, Nino; Richert, Sabine; Limburg, Bart; Clarke, Simon J.; Anderson, Harry L.; Timmel, Christiane R.; Jeschke, Gunnar
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 22(2019)
• Page Start: 11676
• Page End: 11688
• Publication Date: 2019-05-28
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp01760g
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The pulse EPR method ELDOR-detected NMR gives information about electron–electron couplings in Cu(ii ) porphyrin dimers. 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 meso – meso 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 63 Cu and 65 Cu 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.