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A Site-Specific Study of the Magnetic Field-Dependent Proton Spin Relaxation of an Iridium N-Heterocyclic Carbene Complex

  • Andrey N. Pravdivtsev , Alexandra V. Yurkovskaya , Pavel A. Petrov and Konstantin L. Ivanov EMAIL logo
Published/Copyright: October 22, 2016
Zeitschrift für Physikalische Chemie
From the journal Zeitschrift für Physikalische Chemie Volume 231 Issue 4

Abstract

We report a study of proton spin relaxation of an Iridium N-heterocyclic carbene complex [Ir(COD)(IMes)Cl] complex (where COD=1,5-cyclooctadiene, Imes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). This compound is a pre-catalyst of the most efficient complex allowing the signal amplification by reversible exchange (SABRE) effect, relevant for enhancing weak signals in nuclear magnetic resonance (NMR). An important feature of the study is a combination of relaxation measurements over a wide field range with high-resolution NMR detection. As a result, we are able to measure nuclear magnetic relaxation dispersion (NMRD) curves in the field range 0.1 mT–16.4 T (corresponding to the frequency range 4 kHz–700 MHz) for individual protons in the complex under study. This attractive possibility enables determination of the motional correlation times, τc, for the individual protons by analyzing the features in the NMRD curves (increase of the relaxation times) appearing at the magnetic fields where ωτc≈1 (here ω is the proton Larmor precession frequency at a given field strength). The following correlation times were determined: (1.3±0.1) ns for the protons of imidazol-2-ylidene, (0.96±0.1) ns for the ortho-protons of two phenyl moieties and (0.95±0.2) ns for the protons of methyl groups. Additionally, we report low-field features coming from “strong coupling” of the protons. One should note that such features must not be misinterpreted by associating them with motional features. From the low-field features we obtain consistent estimates for the proton spin-spin interactions. The analysis of motional correlation times is also of importance for interpretation of spin order transfer from parahydrogen to various substrates in transient organometallic complexes (termed the SABRE effect) at high magnetic field.

Keywords: correlation times; NMRD; spin relaxation; strong coupling

Dedicated to: Kev Salikhov on the occasion of his 80th birthday.

Acknowledgments

This work has been supported by the Russian Foundation for Basic Research (grants No. 15-33-20716, 16-33-00679). We acknowledge FASO of Russia (project No. 0333-2014-0001) for providing access to NMR facilities. We are thankful to one of the reviewers for valuable comments concerning spectral exchange caused by rotations of the benzene rings.

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Received: 2016-7-9
Accepted: 2016-9-28
Published Online: 2016-10-22
Published in Print: 2017-4-1

©2017 Walter de Gruyter GmbH, Berlin/Boston

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  2. Preface
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  7. Natural Abundance Nitrogen-15 NMR in Thermotropic Liquid Crystals With Cyano-Group
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  9. THz ESR study of Spinel Compound GeCo2O4
  10. Self-Association of Glycyrrhizic Acid. NMR Study
  11. A Site-Specific Study of the Magnetic Field-Dependent Proton Spin Relaxation of an Iridium N-Heterocyclic Carbene Complex
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https://doi.org/10.1515/zpch-2016-0849
Keywords for this article
correlation times; NMRD; spin relaxation; strong coupling

Articles in the same Issue

  1. Frontmatter
  2. Preface
  3. Basic and Combination Cross-Features in X- and Q-band HYSCORE of the 15N Labeled Bacteriochlorophyll a Cation Radical
  4. An EPR Study of Small Magnetic Nanoparticles
  5. Magnetic Resonance Study of the Spin-1/2 Quantum Magnet BaAg2Cu[VO4]2
  6. Triarylmethyl Radicals: An EPR Study of 13C Hyperfine Coupling Constants
  7. Natural Abundance Nitrogen-15 NMR in Thermotropic Liquid Crystals With Cyano-Group
  8. Surface Hydroxyl OH Defects of η-Al2O3 and χ-Al2O3 by Solid State NMR, XRD, and DFT Calculations
  9. THz ESR study of Spinel Compound GeCo2O4
  10. Self-Association of Glycyrrhizic Acid. NMR Study
  11. A Site-Specific Study of the Magnetic Field-Dependent Proton Spin Relaxation of an Iridium N-Heterocyclic Carbene Complex
  12. Multifrequency Multiresonance EPR Investigation of Halogen-bonded Complexes Involving Neutral Nitroxide Radicals
  13. Electron Paramagnetic Resonance and DFT Analysis of the Effects of Bulky Perfluoroalkyl Substituents on a Vanadyl Perfluoro Phthalocyanine
  14. Coordination of the Mn4+-Center in Layered Li[Co0.98Mn0.02]O2 Cathode Materials for Lithium-Ion Batteries
  15. Triarylmethyl Radical: EPR Signal to Noise at Frequencies between 250 MHz and 1.5 GHz and Dependence of Relaxation on Radical and Salt Concentration and on Frequency
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