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Spin-spin coupling constants transmitted through Ir-H...H-N dihydrogen bonds
Malgorzata Olejniczak1, Magdalena Pecul
1Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
Summary
Relativistic effects significantly impact NMR shielding constants in iridium complexes with dihydrogen bonds. Spin-orbit effects are more influential on shielding than on spin-spin coupling, offering insights into molecular structure.
Area of Science:
- Computational chemistry
- Nuclear Magnetic Resonance (NMR) spectroscopy
- Relativistic quantum mechanics
Background:
- NMR spectroscopy is crucial for determining molecular structure.
- Heavy metal complexes, such as those involving iridium, exhibit unique electronic properties.
- Intramolecular hydrogen bonding, specifically dihydrogen bonds, can influence spectroscopic parameters.
Purpose of the Study:
- To investigate the impact of relativistic effects on NMR shielding tensors and spin-spin coupling constants in iridium complexes.
- To analyze the transmission of NMR couplings through Ir-H...H-N dihydrogen bonds.
- To assess the sensitivity of NMR parameters to the H-H distance in dihydrogen bonds.
Main Methods:
- Density Functional Theory (DFT) with the Zeroth-Order Regular Approximation (ZORA) methodology.
- Calculation of NMR shielding tensors and spin-spin coupling constants.
- Modeling of six-coordinated iridium complexes with dihydrogen bonding.
Main Results:
- Spin-orbit relativistic effects have a greater influence on NMR shielding constants than on spin-spin coupling constants.
- Calculated through-space (1h)J(HH) coupling constants (1.6-7.9 Hz) agree well with experimental values (2-5 Hz) for H(a)-H(b) distances < 2.0 Å.
- Significant (2h)J(NH) couplings (-5.1 to -7.1 Hz) were predicted, accessible with 15N-labeled compounds.
Conclusions:
- NMR parameters, particularly spin-spin coupling constants and the shielding tensor of H(a), are sensitive probes of H(a)-H(b) distances in dihydrogen bonds.
- These NMR properties can serve as valuable tools for determining molecular structures.
- Relativistic effects are important for accurate NMR calculations in heavy metal systems.
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