Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication

The hexacoordinated antimony(V) dication (ppy)₃Sb]²⁺ ( 1 ]²⁺; ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor–acceptor interactions, has been isolated as its hexachloroantimonate salt 1 ]SbCl₆]₂, prepared by the oxidative addition of chlorine to the neutral stibine (ppy)₃Sb] ( 1 ), followed by the abstraction of chloride. Air-stable 1 ]SbCl₆]₂ exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the ¹H and ¹³C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for 1 ]SbCl₆]₂ by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature ¹H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication 1 ]²⁺ is the first 12–Sb–6]²⁺ chemical species to have been structurally determined.