Extreme NMR shielding in fluoro-nitrogen cations

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• The shortest experimentally confirmed nitrogen-fluorine (N-F) bond is 1.2461(10) Å in NNF+.
• Accurate prediction of N-F bond lengths and NMR properties is crucial for understanding these compounds.

Purpose of the Study:

• To computationally investigate the structure and NMR shielding of N-F containing cations.
• To predict novel N-F bond lengths and extreme NMR chemical shifts.

Main Methods:

• Extensive *ab initio* calculations using CCSD(T)-F12b/cc-pVQZ-F12 for geometry optimization.
• Composite NMR shielding calculations including coupled-cluster expansions up to CCSDTQP and basis sets up to aug-cc-pCV8Z.
• Inclusion of vibrational and relativistic corrections for enhanced accuracy.

Main Results:

• Optimized geometries suggest shorter N-F bonds in HNF+ (1.236 Å) and NF2+ (1.098 Å) than experimentally known.
• Predicted 19F NMR chemical shifts for HNF+ (1628.9 ppm) and NH2F2+ (1298.0 ppm) are the largest ever reported.
• An extreme 15N chemical shift of -1283.07 ppm is predicted for HNF+.

Conclusions:

• State-of-the-art theoretical techniques provide near-quantitative accuracy for N-F cation properties.
• The study provides accurate NMR properties for isolated and unknown N-F cations.
• Findings can guide and supplement experimental NMR studies of N-F cations.