Nuclear charge-distribution effects on the NMR spectroscopy parameters.

Area of Science:

• Computational Chemistry
• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Quantum Chemistry

Background:

• Nuclear magnetic shielding (σ) and indirect nuclear spin J-coupling are key NMR parameters.
• The influence of nuclear charge-distribution models on these parameters is not fully understood.
• Relativistic effects are known to impact electronic structure calculations.

Purpose of the Study:

• To systematically investigate the influence of nuclear charge-distribution models (Gaussian and point-like) on NMR spectroscopic parameters.
• To assess the role of relativistic effects in nuclear charge-distribution effects (NChDE).
• To analyze the sensitivity of nuclear magnetic shielding and J-coupling to the chosen nuclear model.

Main Methods:

• Theoretical calculations of NMR spectroscopic parameters (nuclear magnetic shielding and J-coupling).
• Comparison of results using different nuclear charge-distribution models (Gaussian vs. point-like).
• Inclusion of relativistic and non-relativistic (NR) computational regimes.

Main Results:

• Relativistic effects significantly enhance nuclear charge-distribution effects (NChDE) on NMR parameters.
• J-couplings are more sensitive to the nuclear model than shieldings in both relativistic and NR calculations.
• Largest NChDE observed for J(Pb-I) in PbIH(3) (11% variation) and J(Pb-H) (9% variation); significant NChDE also found for σ(Sn) and J(Sn-H) in tin compounds.

Conclusions:

• The choice of nuclear charge-distribution model has a substantial impact on calculated NMR parameters, particularly when relativistic effects are considered.
• Nuclear charge-distribution effects (NChDE) are more pronounced in J-couplings than in shieldings.
• These findings highlight the importance of selecting appropriate nuclear models for accurate NMR spectroscopic predictions, especially in heavy-element systems.