The LRESC-Loc Model to Analyze Magnetic Shieldings with Localized Molecular Orbitals

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Relativistic effects significantly influence NMR magnetic shieldings in heavy-atom (HA) molecules.
• The linear response with elimination of small components (LRESC) model effectively describes these electronic mechanisms.
• Understanding these effects is crucial for interpreting NMR data in systems with heavy elements.

Purpose of the Study:

• Introduce a novel LRESC model formulation using localized molecular orbitals (LMOs), termed LRESC-Loc.
• Analyze the electronic origins of relativistic effects on NMR shieldings in HA-containing molecules.
• Characterize spin-orbit (SO) and non-SO mechanisms based on LMO contributions.

Main Methods:

• Developed LRESC-Loc, a version of the LRESC model utilizing LMOs.
• Examined relativistic effects in molecules with heavy elements from groups IB to VIIA.
• Decomposed relativistic effects into non-ligand-dependent and ligand-dependent contributions.

Main Results:

• LRESC-Loc provides insights into the electronic origins of relativistic effects on NMR shieldings.
• The SO mechanism shows a clear dependence on lone-pair (LP) LMOs (LPσ and LPπ) when present.
• Non-SO mechanisms are primarily influenced by other LMOs, distinct from lone pairs.

Conclusions:

• The LRESC-Loc model offers a new perspective on analyzing relativistic effects in HA molecules.
• SO mechanisms can characterize lone-pair interactions, while non-SO mechanisms characterize covalent and close-shell interactions.
• The findings align with previous studies, offering a more detailed analysis of electronic origins.