Abstract
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) ].