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Paramagnetic Enhancement of Nuclear Spin-Spin Coupling.
Peter John Cherry1, Syed Awais Rouf2, Juha Vaara2
1Institute of Inorganic Chemistry, Slovak Academy of Sciences , Dúbravská cesta 9, SK-84536 Bratislava, Slovakia.
Journal of Chemical Theory and Computation
|January 20, 2017
Summary
We derived paramagnetic enhancement for nuclear magnetic resonance (NMR) spin-spin coupling, influenced by hyperfine coupling and zero-field splitting. This effect becomes more significant with increasing nuclear distances, offering new insights for paramagnetic NMR experiments.
Area of Science:
- Quantum Chemistry
- Magnetic Resonance Spectroscopy
- Computational Chemistry
Background:
- Nuclear Magnetic Resonance (NMR) spin-spin coupling is a fundamental property in chemistry.
- Paramagnetic substances introduce unique interactions affecting NMR signals.
- Understanding these interactions is crucial for analyzing complex molecular systems.
Purpose of the Study:
- To derive and compute the paramagnetic enhancement of NMR spin-spin coupling.
- To investigate the role of hyperfine coupling (HFC) and zero-field splitting (ZFS) tensors.
- To demonstrate the significance of this enhancement in various paramagnetic systems.
Main Methods:
- Theoretical derivation of paramagnetic enhancement.
- Combination of density-functional theory (DFT) and correlated ab initio calculations.
- Calculation of HFC and ZFS tensors, including relativistic effects using two distinct methods.
Main Results:
- The paramagnetic enhancement is formally analogous to hyperfine contributions to NMR shielding.
- Calculations were performed for 3d metallocenes, Cr(acac)2, Co(II) pyrazolylborate, and Gd-DOTA.
- Relativistic effects on HFC tensors were assessed using both perturbation and four-component approaches.
Conclusions:
- Paramagnetic enhancement is independent of the distance between coupled nuclei.
- It reflects the strength and orientation of HFCs relative to spin density.
- This enhancement becomes more important for larger internuclear distances or weak conventional couplings, with potential applications in advanced paramagnetic NMR.
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