An Organogold(III) Difluoride with a trans Arrangement

The trans isomer of the organogold(III) difluoride complex [PPh₄ ][(CF₃ )₂ AuF₂ ] has been obtained in a stereoselective way and in excellent yield by reaction of [PPh₄ ][CF₃ AuCF₃ ] with XeF₂ under mild conditions. The compound is both thermally stable and reactive. Thus, the fluoride ligands are stereospecifically replaced by any heavier halide or by cyanide, the cyanide affording [PPh₄ ][trans-(CF₃ )₂ Au(CN)₂ ]. The organogold fluoride complexes [CF₃ AuF_x ]^- (x=1, 2, 3) have been experimentally detected to arise upon collision-induced dissociation of the [trans-(CF₃ )₂ AuF₂ ]^- anion in the gas phase. Their structures have been calculated by DFT methods. In the isomeric forms identified for the open-shell species [CF₃ AuF₂ ]^- , the spin density residing on the metal center is found to strongly depend on the precise stereochemistry. Based on crystallographic evidence, it is concluded that Auⁱⁱⁱ and Agⁱⁱⁱ have similar covalent radii, at least in their most common square-planar geometry.