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, D 2h -symmetry halogenbridged geometry, with the gold atom in an almost square-planar coordination. The geometrical parameters from electron diffraction (r g and ∠ R ) are: Au-Cl t , 2.236 ( 0.013 Å; Au-Cl b , 2.355 ( 0.013 Å; ∠Cl t -Au-Cl t , 92.7 ( 2.5°; and ∠Cl b -Au-Cl b , 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 AuCl 3 ; both have C 2V -symmetry structures due to Jahn-Teller distortion. CASSCF calculations show that the triplet D 3h -symmetry structure lies ∼29 kcal/mol above the 1 A 1 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 AuCl 3 is smaller than that of AuF 3 , and the possible reasons are discussed. The structure of the AuCl 4ion has also been calculated, the latter both in planar, D 4h , and tetrahedral, T d , arrangements. The tetrahedral configuration of AuCl 4is subject to Jahn-Teller effect, which leads to a complicated potential energy surface. The factors leading to the planar geometry of AuCl 4and Au 2 Cl 6 are discussed. The frequently suggested dsp 2 hybridization as a possible cause for planarity is not supported by this study. The geometries of AuCl and Au 2 Cl 2 have also been calculated. The very short Au‚‚‚Au distance in the latter, similarly to Au 2 F 2 , is indicative of the aurophilic interaction.

Application of heterogeneous gold catalysis with increased durability: Oxidation of CO and hydrocarbons at low temperature

“…This is due to the ease with which gold and chloride ions combine to form bridges, favouring the growth of the particles upon heating (13). Furthermore, chlorine also has a poisoning effect on the CO oxidation reaction by blocking the active sites (14).…”

Experimental Evidence for a Jahn–Teller Distortion in AuCl3

“…[1][2][3][4] Advances in gasphase (mass-spectrometry) experiments [5] and the theoretical importance of relativistic effects in gold chemistry [6] have recently been reviewed. The common oxidation states for gold are Au III and Au I , with Au II being comparatively rare.…”

Experimental and theoretical studies of diatomic gold halides

“…The experimental characterization of the gaseous gold halides is more difficult [2], however, and only recently decisive experimental measurements of some spectroscopic properties of AuF [3,4], AuCl [5][6][7], AuBr [5], and AuI [8] have been published. As far as experimental determinations of the bond dissociation energies (BDEs) of AuX diatomics are concerned, only some extrapolations from spectroscopy [6,8] and a few ion/ molecule bracketing data are available [9,10].…”