Solid-State ¹⁹F NMR Chemical Shift in Square-Planar Nickel-Fluoride Complexes Linked by Halogen Bonds.

Area of Science:

• Solid-state chemistry
• Nuclear Magnetic Resonance (NMR) spectroscopy
• Computational chemistry

Background:

• Halogen bonding (XB) is a crucial noncovalent interaction, yet its NMR signature remains understudied.
• Solid-state NMR (SSNMR) chemical shift tensor analysis offers insights into XB interactions.
• Previous experimental work measured ¹⁹F SSNMR chemical shifts in square-planar Ni^II complexes forming XBs.

Purpose of the Study:

• To computationally model and analyze ¹⁹F SSNMR chemical shifts in Ni^II-L₂-iodoaryl-fluoride complexes.
• To elucidate the origin of ¹⁹F NMR shielding/deshielding effects caused by halogen bonding.
• To investigate the influence of crystal packing versus XB interactions on NMR signatures.

Main Methods:

• Computational protocol for modeling ¹⁹F SSNMR chemical shifts.
• Calculations performed using periodic and molecular models.
• Analysis using the 2c-ZORA level of theory.

Main Results:

• Crystal packing has minimal impact on NMR signatures; molecular models suffice for analysis.
• The 2c-ZORA method accurately reproduces the high fluoride shielding and its tensor components.
• Shielding originates from Ni(3d)/F(2p) orbital coupling with the vacant σ_Ni-F^* orbital.
• Halogen bonding increases the energy gap, leading to fluoride deshielding.

Conclusions:

• ¹⁹F SSNMR chemical shifts in these complexes are primarily dictated by halogen bonding.
• The computational approach successfully rationalizes the observed NMR spectral features.
• The findings provide a deeper understanding of halogen bond interactions via NMR spectroscopy.