Homoleptic teflate coordination at platinum(iv): synthesis and characterization of [Pt(OTeF5)6]2-, and covalency trends revealed by the OSLO method.

The pentafluoroorthotellurate group (teflate, -OTeF5) is a unique ligand in transition metal and main group chemistry that combines exceptionally strong electron-withdrawing properties, comparable to those of fluorine, with substantial steric demand. However, its coordination behaviour in transition metal complexes remains poorly understood, in part due to the scarcity of homoleptic transition metal teflate complexes, particularly for late transition metals. By reacting [NEt4]2[PtCl6] and ClOTeF5 under solvent-free conditions, we have synthesized the first hexacoordinate homoleptic transition-metal teflate complex, [NEt4]2[Pt(OTeF5)6]. This compound exhibits an extraordinary stability: it is bench-stable, resistant toward hydrolysis and alcoholysis, and displays a high thermal decomposition temperature of 200 °C. In the crystallographically determined molecular structure, the O-Te bond lengths, together with the ν(O-Te) stretching vibration in the IR spectrum, point toward a pronounced covalent contribution in the Pt-O interaction. To better understand the bonding situation and the electronic stucture of the complex, the system was further analysed using energy decomposition analysis coupled with natural orbitals for chemical valence (EDA-NOCV), quantum theory of atoms in molecules (QTAIM) and the oxidation state localized orbital (OSLO) method. The latter unambiguously assigns an oxidation state of +IV to the platinum centre. A linear correlation between the fragment orbital localization index (FOLI) value of the M-O σ bonding orbital of various homoleptic metal teflate complexes and their experimentally determined mean O-Te bond length was identified. This relationship was subsequently extended to homoleptic main-group teflate compounds, highlighting the general applicability of this approach for assessing the nature of element-teflate bonds.