Structure of the SO(2)F(-) anion, a problem case.

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Computational Chemistry

Background:

• Previous room-temperature crystal structures of SO(2)F(-) salts showed geometries inconsistent with theoretical calculations.
• This discrepancy highlighted a need for more accurate structural determination of the SO(2)F(-) anion.

Purpose of the Study:

• To resolve the discrepancy between experimental and theoretical geometries of SO(2)F(-).
• To accurately determine the crystal structure of SO(2)F(-) by studying various salts at low temperatures and accounting for disorder.

Main Methods:

• Synthesis and low-temperature crystal structure analysis of new and known SO(2)F(-) salts, including [(CH(3))(2)N](3)SO(+) and K(+) salts.
• Confirmation of theoretical calculations (RHF, B3LYP, CCSD(T)) using different basis sets.
• Analysis of structural disorder and extrapolation to zero disorder for bond length and angle determination.

Main Results:

• All studied SO(2)F(-) salts exhibited varying degrees of oxygen/fluorine and oxygen-site disorder.
• The [(CH(3))(2)N](3)SO(+) salt at 113 K showed minimal disorder, yielding S-F and S-O bond lengths differing by 17 pm and O-S-O/F-S-O angles by 6 degrees.
• Extrapolated geometries closely matched theoretical predictions; vibrational frequencies also showed good agreement with calculations and isoelectronic ClO(2)F.

Conclusions:

• The study confirms the validity of theoretical predictions for SO(2)F(-) geometry, particularly regarding the weak S-F bond (force constant 1.63 mdyn/A).
• Structural disorder in previously reported room-temperature studies led to inaccurate geometric parameters.
• The S-F bond is weak and strongly coupled with SO(2) deformation modes, appearing in the lowest vibrational frequencies.