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

Abstract

The pentafluoroorthotellurate group (teflate, OTeF5 ) is considered as a bulky analogue ofbfluoride, yet its coordination behavior in transition-metal complexes is not fully understood. By reaction of [CoCl4 ]2– and neat ClOTeF5 , we have synthesized the first cobalt teflate complex, [Co(OTeF5 )4 ]2– , which exhibits moisture-resistant Co–OTeF5 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 d7 system with a quartet (S = 3/2) ground state. A comparative bonding analysis of the (pseudo)tetrahedral [CoX4 ]2– anions (X = OTeF5 , F, Cl) revealed that the strength of the Co–X interaction is similar in the three cases, being the strongest in [Co(OTeF5 )4 ]2– . In addition, an analysis of the charge of the Co center reinforced the similar electron-withdrawing properties of the teflate and the fluoride ligands. Therefore, the [Co(OTeF5 )4 ]2– anion constitutes an analogue of the polymeric [CoF4 ]2– in terms of electronic properties, but with a monomeric structure.