Intriguing Gold TrifluorideMolecular Structure of Monomers and Dimers: An Electron Diffraction and Quantum Chemical Study

The molecular geometry of monomeric and dimeric gold trifluoride, AuF 3 and Au 2 F 6, has been determined by gas-phase electron diffraction and high-level quantum chemical calculations. Both experiment and computation indicate that the ground-state structure of AuF 3 has C 2 v symmetry, rather than 3-fold symmetry, with one shorter and two longer Au−F bonds and an almost T-shaped form, due to a first-order Jahn−Teller effect. CASSCF calculations show the triplet D 3 h symmetry structure, 3 A ‘, to lie about 42 kcal/mol above the 1 A 1 symmetry ground state and the D 3 h symmetry singlet, 1 A ‘, even higher than the triplet state, by about a further 13 kcal/mol. The molecule has a typical “Mexican-hat”-type potential energy surface with three equal minimum-energy structures around the brim of the hat, separated by equal-height transition structures, about 3.6 kcal/mol above the minimum energy. The geometry of the transition structure has also been calculated. The dimer has a D 2 h symmetry planar, halogen-bridged geometry, with the gold atom having an approximately square-planar coordination, typical for d 8 transition metals. The geometries of AuF and Au 2 F 2 have also been calculated. The very short Au···Au separation in Au 2 F 2 is indicative of the so-called aurophilic interaction. This effect is much less pronounced in Au 2 F 6 .