Synthesis and structures of antimony trifluoride complexes with N-heterocyclic ligands

The reaction of SbF3 with 2,2′-bipyridyl in anhydrous methanol produces [SbF3(bipy)]·[SbF3(MeOH)], the structure of which comprises co-crystallised neutral centrosymmetric [F2(bipy)Sb(μ-F)2Sb(bipy)F2] dimers, with neutral four-coordinate [SbF3(MeOH)] units. These are linked by longer fluorine contacts, each antimony achieving a distorted seven-coordinate geometry. [SbF3(bipy)·H2O] was obtained from iPrOH solution, but hydrolysis in solution readily forms [bipyH][Sb2F7]. [SbF3(phen)], also containing seven-coordinate antimony, is produced from SbF3 and 1,10-phenanthroline in MeOH, but [SbF3(2,2′6′,2″-terpyridyl)] has a six-coordinate antimony centre (pentagonal pyramidal) with no significant intermolecular contacts to neighbouring molecules. In [SbF3(pyNO)] polymeric chains involving bridging fluorine and pyridine-N-oxide are present, again resulting in a very distorted seven-coordinate geometry at Sb. The geometries present in these N-heterocycle adducts are compared with those in pnictogen oxide and crown ether complexes. Attempts to isolate complexes of SbF3 with soft donors (PMe3, SMe2 etc.) have been unsuccessful, as were attempts to form complexes with SbF3 functioning as a Lewis base towards metal carbonyls.

The crystal structures of SbF3 complexes with heterocyclic nitrogen ligands show a pyramidal SbF3 core with longer bonds to the neutral ligand and longer Sb⋯F contacts typically completing a distorted seven-coordination at Sb.Figure optionsDownload as PowerPoint slideHighlights
► Antimony fluoride complexes with N-heterocycles are polymeric via F-bridges.
► The favoured coordination number at antimony is seven.
► Distorted geometries show a stereochemically active lone pair present.
► Structures are compared with those with pnictogen oxides and crown ethers.