Are the NF4+ cations in NF4BF4 really nontetrahedral?

Area of Science:

• Solid-state chemistry
• Inorganic chemistry
• Crystallography

Background:

• Previous studies suggested the existence of non-tetrahedral ammonium tetrafluoride (NF4+) cations in solid salts.
• Discrepancies existed between different spectroscopic and crystallographic analyses of NF4+ salts.

Purpose of the Study:

• To reexamine the crystal structure of NF4BF4.
• To clarify the cation geometry in solid NF4+ salts.
• To reconcile conflicting data from vibrational spectra, X-ray crystallography, and NMR spectroscopy.

Main Methods:

• Low-temperature X-ray structure determination.
• Solid-state 19F Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy.
• Analysis of existing vibrational spectra data.

Main Results:

• The low-temperature X-ray structure and 19F MAS NMR spectra are consistent with tetrahedral NF4+ cations.
• Previous findings of non-tetrahedral NF4+ cations are attributed to incorrectly solved crystal structures.
• Disorder and twinning in crystal structures may have contributed to erroneous interpretations.

Conclusions:

• Solid NF4+ salts exclusively contain tetrahedral NF4+ cations.
• Over-reliance on potentially flawed crystal structures can lead to incorrect theoretical conclusions.
• Accurate structural determination is crucial for understanding chemical species and their properties.