Silver(III) is the highest oxidation state currently available for the element. Ag(III) is a powerful oxidant with which a limited number of ligands are compatible. Simple compounds such as AgCl₃, AgBr₃, or AgI₃ are still unknown, as are the corresponding [AgX₄]⁻ ions.

Babil Menjón, CSIC–Universidad de Zaragoza, Spain, and colleagues have isolated the mixed halide organocomplexes [(CF₃)₂AgCl₂]^– and [(CF₃)₂AgBr₂]^– as their trans isomers. The team added the homoleptic organosilver(I) compound [PPh₄][CF₃AgCF₃] to a solution of Cl₂ to obtain [PPh₄][trans-(CF₃)₂AgCl₂]. The bromo-derivative [PPh₄][trans-(CF₃)₂AgBr₂] was prepared via a reaction with Br₂ following a similar procedure.

The resulting complexes are square-planar, and they are prone to ligand association to form complexes such as [PPh₄]₂[(CF₃)₂AgBr₃] (anion pictured). The latter complex is unusual in that it is the first Ag(III) compound with trigonal symmetry and also the first five-coordinate compound with an inverted ligand field.

• The First Five‐coordinate Compound with Inverted Ligand Field: An Unprecedented Geometry for Silver(III),
  Babil Menjón, Daniel Joven-Sancho, Miguel Baya, Antonio Martín, Jesús Orduna,
  Angew. Chem. Int. Ed. 2021.
  https://doi.org/10.1002/anie.202112449