The stability of gold iodides in the gas phase and the solid state

The stability of gold iodides in the oxidation state +I and +III is investi gated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The c alculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at th e relativistic level, whilst at the nonrelativistic level the complex of tw o iodine molecules weakly bound to both gold atoms in Au2I2 is energeticall y preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I-2 Will make it difficult to isolate this species in the soli d state as (possibly) Au2I6 or detect it by matrix-isolation techniques. Th e monomer Au-3, is Jahn-Teller distorted from the ideal trigonal planar (D- 3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I-2 weakly bound to AuI . Relativistic effects turn AuI3 from a static Jahn-Teller system to a dyna mic one. For the yet undetected gas-phase species AuI accurate coupled-clus ter calculations for the potential energy curve are used to predict vibrati onal-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.