Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry.

The pentafluoroorthotellurate group (teflate, OTeF 5 ) is able to form species, for which only the fluoride analogues are known. Despite nickel fluorides being widely investigated, nickel teflates have remained elusive for decades. By reaction of [NiCl 4 ] 2- and neat ClOTeF 5 , we have synthesized the homoleptic [Ni(OTeF 5 ) 4 ] 2- anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF 4 ] 2- . This high-spin complex has allowed the study of the electronic properties of the teflate group, which can be classified as a weak/medium-field ligand, and therefore behaves as the fluoride analogue also in ligand-field terms. The teflate ligands in [NEt 4 ] 2 [Ni(OTeF 5 ) 4 ] are easily substituted, as shown by the formation of [Ni(NCMe) 6 ][OTeF 5 ] 2 by dissolving it in acetonitrile. Nevertheless, careful reactions with other conventional ligands have enabled the crystallization of nickel teflate complexes with different coordination geometries, i.e. [NEt 4 ] 2 [trans-Ni(OEt 2 ) 2 (OTeF 5 ) 4 ] or [NEt 4 ][Ni(bpyMe 2 )(OTeF 5 ) 3 ].