The limits of copper oxidation states from density functional theory computations: Fluoro-copper complexes, [CuFn]x, where n = 1 through 6 and x = 3+ through 5−

Density functional theory calculations, at the ωB97X-D/6-311+G* level of theory, were performed on homoleptic fluoro-copper complexes [CuF_n]^x, n = 1 through 6 and x = 3+ through 5−, to determine the highest positive and lowest negative copper oxidation states that can be supported in these complexes. Only singlet and doublet spin states were investigated. All fluoro-copper stoichiometries stabilized copper(III) or greater. However, some stoichiometries stabilized oxidation states up to copper(VI), and the greatest positive copper oxidation state was copper(VIII) in the distorted octahedral [CuF₆]²⁺ cation. Oxidation states as negative as copper(–IV) in the diatomic [CuF]⁵⁻ anion and copper(–III) in the triatomic [CuF₂]⁵⁻ were also observed as optimized minima, although no negative oxidation states were calculated to exist for fluoro-copper complexes containing more than two fluorine atoms. No singlet or doublet fluoro-copper complexes with charges more positive than 3+, more negative than 5−, or of Cu(VII), could be optimized.