Structural variations and bonding in gold halides: A quantum chemical study of monomeric and dimeric gold monohalide and gold trihalide molecules, AuX, Au2X2, AuX3, and Au2X6 (X = F, Cl, Br, I)

The molecular structures of all gold mono- and trihalides and of their dime rs have been calculated at the B3LYP, MP2, and CCSD(T) levels of theory by using relativistic pseudopotentials for all atoms except fluorine. Our comp utations support the experimental observation that the relative stability o f the monohalides increases from the fluoride toward the iodide, while the stability trend of the trihalides is the opposite. The potential energy sur face (PES) of all gold trihalides has been investigated. These molecules ar e typical Jahn-Teller systems; the trigonal planar D-3h-symmetry geometry d oes not correspond to the minimum energy structure for any of them. At the same time, the amount and character of their Jahn-Teller distortion changes gradually from AuF3 to AuI3. The minimum energy geometry is a T-shaped str ucture for AuF3 and AuCl3, with a Y-shaped transition-state structure. For AuI3, the Y-shaped structure lies lower than the T-shaped structure on the PES. For AuBr3 and AuI3, neither of them is the global minimum but instead an L-shaped structure, which lies outside the Jahn-Teller PES. This structu re can be considered to be a donor-acceptor system, or a closed-shell inter action, with I-2 acting as donor and AuI as acceptor. The dimers of gold mo nohalides have very short gold-gold distances and demonstrate the aurophili c interaction. The dimers of the trihalides are planar molecules with two b ridging halogen atoms.