Further Perspectives on the Teflate versus Fluoride Analogy: The Case of a Co(II) Pentafluoroorthotellurate Complex.

The pentafluoroorthotellurate group (teflate, OTeF 5 ) is considered as a bulky analogue of fluoride, yet its coordination behavior in transition metal complexes is not fully understood. By reaction of [CoCl 4 ] 2- and neat ClOTeF 5 , we synthesized the first cobalt teflate complex, [Co(OTeF 5 ) 4 ] 2- , which exhibits moisture-resistant Co-OTeF 5 bonds. Through a combined experimental and theoretical (DFT and NEVPT2) study, the properties and electronic structure of this species have been investigated. It exhibits a distorted tetrahedral structure around the cobalt center and can be described as a d 7 system with a quartet ( S = 3/2) ground state. A comparative bonding analysis of the (pseudo)tetrahedral [CoX 4 ] 2- anions (X = OTeF 5 , F, Cl) revealed that the strength of the Co-X interaction is similar in the three cases, being the strongest in [Co(OTeF 5 ) 4 ] 2- . In addition, an analysis of the charge of the Co center reinforced the similar electron-withdrawing properties of the teflate and fluoride ligands. Therefore, the [Co(OTeF 5 ) 4 ] 2- anion constitutes an analogue of the polymeric [CoF 4 ] 2- in terms of electronic properties, but with a monomeric structure.