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

Abstract

Antimony pentafluoride is a strong Lewis acid and fluoride-ion acceptor that has not previously demonstrated any discreet fluoride-ion donor properties. The first donor-stabilised [SbF4 ]+ cations were prepared from the autoionisation of SbF5 in the presence of bidentate N-donor ligands 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen) as their [SbF6 ]- salts. The [SbF4 (N-N)][Sb2 F11 ] (N-N=bipy, phen) salts were synthesised by the addition of one equivalent of SbF5 ⋅SO2 to [SbF4 (N-N)][SbF6 ] in liquid SO2. The salts show remarkable stability and were characterised by Raman spectroscopy and multinuclear NMR spectroscopy. The crystal structures of [SbF4 (phen)][SbF6 ] ⋅ 3CH3 CN and [SbF4 (phen)][SbF6 ] ⋅ 2SO2 were determined, showing distorted octahedral cations. DFT calculations and NBO analyses reveal that significant degree of electron-pair donation from N to Sb stabilizes [SbF4 ]+ with the Sb-N bond strength being approximately two thirds of that of the Sb-F bonds in these cations and the cationic charge being primarily ligand-centred.