Donor-Stabilised [SbF₄ ]⁺ : SbF₅ as a Fluoride-Ion Donor

Area of Science:

• Inorganic Chemistry
• Fluorine Chemistry
• Coordination Chemistry

Background:

• Antimony pentafluoride (SbF5) is known as a potent Lewis acid and fluoride acceptor.
• SbF5 has not previously exhibited fluoride-ion donor capabilities.
• Donor-stabilized cations of antimony(V) have not been previously reported.

Purpose of the Study:

• To synthesize and characterize the first donor-stabilized [SbF4]+ cations.
• To explore the unique fluoride-ion donor properties of antimony pentafluoride in the presence of N-donor ligands.
• To investigate the structural and electronic properties of these novel cationic species.

Main Methods:

• Autoionization of SbF5 in the presence of bidentate N-donor ligands (2,2'-bipyridine and 1,10-phenanthroline).
• Synthesis of [SbF4(N-N)][Sb2F11] salts via reaction of SbF5·SO2 with [SbF4(N-N)][SbF6] in liquid SO2.
• Characterization using Raman spectroscopy, multinuclear NMR spectroscopy, and X-ray crystallography.
• Computational analysis including Density Functional Theory (DFT) and Natural Bond Orbital (NBO) analyses.

Main Results:

• Successful preparation of the first donor-stabilized [SbF4]+ cations, isolated as [SbF4(N-N)][Sb2F11] salts.
• Characterization confirmed the stability of these novel antimony(V) fluoride complexes.
• Crystal structure determination revealed distorted octahedral cations with significant Sb-N bond character.
• DFT and NBO analyses indicated electron-pair donation from the N-donor ligands to the antimony center, stabilizing the [SbF4]+ cation.

Conclusions:

• Antimony pentafluoride can act as a fluoride-ion donor when stabilized by appropriate N-donor ligands.
• The synthesized [SbF4]+ cations represent a new class of antimony(V) compounds with unique bonding characteristics.
• The stabilization mechanism involves significant electron donation from the ligand to the antimony center, influencing the cation's electronic structure and stability.