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 Å; Au-Clb, 2.355 ± 0.013 Å ∠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 CASSCF level. The distortion of AuCl3 is smaller than that of AuF3, and the possible reasons are discussed. The structure of the AuCl4- ion has also been calculated, the latter both in planar, D4h, and tetrahedral, Td, arrangements. The tetrahedral configuration of AuCl4- is subject to Jahn-Teller effect, which leads to a complicated potential energy surface. The factors leading to the planar geometry of AuCl4- and Au2Cl6 are discussed. The frequently suggested dsp2 hybridization as a possible cause for planarity is not supported by this study. The geometries of AuCl and Au2Cl2 have also been calculated. The very short Au···Au distance in the latter, similarly to Au2F2, is indicative of the aurophilic interaction.
ASJC Scopus subject areas
- Colloid and Surface Chemistry