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Molecular Physics
An International Journal at the Interface Between Chemistry and Physics
Volume 111, 2013 - Issue 18-19: Modern EPR Spectroscopy
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Invited Articles

W-band ELDOR-detected NMR (EDNMR) spectroscopy as a versatile technique for the characterisation of transition metal–ligand interactions

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Pages 2788-2808 | Received 30 Apr 2013, Accepted 26 Jul 2013, Published online: 09 Sep 2013
 

Abstract

ELDOR-detected NMR (EDNMR) spectra for a series of hydrated transition metal complexes: MnII(H2O)6, CuII(H2O)6 and VIVO(H2O)5 are reported. All EDNMR experiments were performed at W-band (94 GHz) employing two independent microwave frequencies. A purpose-built broadband microwave resonator (spectral range 300 MHz) was used, sufficient to detect all single quantum nuclear transitions of the three model systems. The EDNMR spectral lineshape observed is essentially the same as in conventional ENDOR (Electron-Nuclear Double Resonance). EDNMR presents two technical advantages over ENDOR for transition metal complexes: (i) enhanced sensitivity, reducing acquisition times by at least one order of magnitude; and (ii) simultaneous detection of transitions from all magnetic nuclei. This includes ligand (1H, 2H, 17O) and metal centred hyperfine couplings. For the latter, both isotropic couplings in the case of the 55Mn complex and highly anisotropic couplings in the case of 51V and 63,65Cu complexes could be resolved. By monitoring the intensity of the EDNMR lines as function of the amplitude of the pumping microwave pulse, transitions from non-equivalent nuclei can be differentiated. Double quantum transitions are also readily identified. In case of the MnII(H217O)6 complex, spectral lines involving the simultaneous pumping of both the 55Mn and 17O nuclear transitions are observed.

Acknowledgements

This work is supported by the Cluster of Excellence RESOLV (EXC 1069) funded by the Deutsche Forschungsgemeinschaft and the Max-Planck-Gesellschaft.

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