Molecular Structure, Bonding, and Jahn−Teller Effect in Gold Chlorides: Quantum Chemical Study of AuCl3, Au2Cl6, AuCl4-, AuCl, and Au2Cl2 and Electron Diffraction Study of Au2Cl6

Abstract

The molecular geometry of dimeric gold trichloride has been determined by gas-phase electron diffraction and high-level quantum chemical calculations. The molecule has a planar, D2h-symmetry halogen-bridged geometry, with the gold atom in an almost square-planar coordination. The geometrical parameters from electron diffraction (rg and ∠α) are: Au−Clt, 2.236 ± 0.013 A; Au−Clb, 2.355 ± 0.013 A; ∠Clt−Au−Clt, 92.7 ± 2.5°; and ∠Clb−Au−Clb, 86.8 ± 1.8° (t, terminal; b, bridging chlorine). Quantum chemical calculations have also been carried out on the ground-state and transition-state structures of monomeric AuCl3; both have C2v-symmetry structures due to Jahn−Teller distortion. CASSCF calculations show that the triplet D3h-symmetry structure lies ∼29 kcal/mol above the 1A1 symmetry ground state. The Mexican-hat-type potential energy surface of the monomer has three equal minimum-energy positions around the brim of the hat, separated by three transition-state structures, ∼6 kcal/mol higher in energy, at the C...