S=N versus S+-N-: an experimental and theoretical charge density study.

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Hypervalent sulfur-nitrogen compounds are widely discussed but their bonding situation remains unclear.
• Understanding these bonds is crucial for advancing inorganic and materials science.

Purpose of the Study:

• To elucidate the bonding situation in hypervalent sulfur-nitrogen species.
• To compare experimental and theoretical charge density distributions and bonding properties.

Main Methods:

• High-resolution low-temperature X-ray diffraction experiments (T = 100 K) on four representative sulfur-nitrogen compounds.
• Gas-phase ab initio calculations for comparative analysis.
• Topological analysis of charge density distributions and Natural Bond Orbital (NBO) / Natural Resonance Theory (NRT) approaches.

Main Results:

• Experimental and theoretical methods agreed on the spatial Laplacian distribution and polarization of sulfur-nitrogen bonds.
• All investigated sulfur-nitrogen bonds exhibit distinct polarization, supporting an S(+)-N(-) formulation.
• Classical double bond formulation for S-N bonds was not supported; sulfur valence expansion was excluded.

Conclusions:

• The bonding in hypervalent sulfur-nitrogen species is best described by polarized S(+)-N(-) bonds, not classical double bonds.
• Theoretical and experimental findings consistently indicate distinct polarization and reject sulfur valence expansion.
• The study provides a clear understanding of bonding modes in diverse sulfur-nitrogen compounds.