Pentaphenylantimony
Pentaphenylantimony is an organoantimony compound containing five phenyl groups attached to one antimony atom. It has formula Sb5.
Structure
The structure of pentaphenylantimony has been the subject of several studies, and a definite ground state remains uncertain. The molecule adopts a roughly square pyramidal shape in the unsolvated crystal. In crystals of the solvate with cyclohexane or tetrahydrofuran, the compound adopts a trigonal bipyramid shape. When dissolved, molecules are also trigonal bipyramidal. According to solution NMR measurements, the phenyl groups all appear to be equivalent, indicating fluxionality.Solid pure pentaphenylantimony forms triclinic crystals in the P space group. The unit cell has a=10.286 b=10.600 and c=13.594 Å, α=79.20° β=70.43° γ=119.52°. The basal Sb-C bond length is 2.216 Å whereas the apex Sb-C length is 2.115 Å.
Reactions
Pentaphenylantimony reacts with a variety of protic reagents. Benzene is one product as well as a tetraphenylantimony compound:Halogens also cleave one Sb-phenyl bond:
When heated, pentaphenylantimony forms triphenylstibine, biphenyl and p-quaterphenyl.
A reaction with carbon tetrachloride yields tetraphenylstibonium chloride, chlorobenzene, and benzene. Some of these reactions may proceed by radical pathways.