THEORETICAL PREDICTION OF THE STRUCTURE AND THE BOND-ENERGY OF THE GOLD(I) COMPLEX AU(+) (H2O)

The Au+ (H2O) complex has been studied by ab initio MO calculations using a relativistic effective core potential with a large polarized basis set. Geometry optimizations at the MP2 and the CISD levels of theory lead to a non-planar C(s)-symmetrical structure 1 with an Au-O bond length of 2.133 angstrom and a hardly distorted water substructure with a wag angle theta(w) of 47-degrees. In contrast to other cationic transition-metal hydrates, the corresponding planar structure 2 with C2v symmetry is slightly higher in energy and exhibits one imaginary frequency (nu = i270 cm-1). Thus 2 is a transition structure and its further analysis reveals that the transition corresponds to the 'umbrella' vibration of the pyramidalized water substructure (1 half arrow right over half arrow left 2). The pyramidalization of 1 can be attributed to re-hybridization of the water molecule upon complexation by the Au+ cation, due to the relativistically enlarged ionization energy of the gold atom. The calculated bond dissociation energies of the Au+ (H2O) complex converges to 36.0 kcal/mol at the CCSD(T) level of theory. Similar energetic and structural results are obtained using a density functional theory approach, i.e. BDE = 37.0 kcal/mol, r(Au-O) = 2.196 angstrom, and theta(w) = 49-degrees.