Photodissociation spectrum and structure of Au4+·H2O clusters

Abstract

The gold–water interaction is essential for a fundamental understanding of the coordination chemistry of gold as well as applied materials sciences. Here isolated Au4+ and Au4+·H2O clusters are characterized with electronic photodissociation spectroscopy and long-range corrected time-dependent density functional theory. Structural information of these clusters is obtained by comparing their photodissociation spectra with the optical absorption spectra calculated for low-energy isomers, which are found with a genetic algorithm coupled to electronic structure methods. For Au4+, the most stable structure is found to be a D2h rhomboid, while a remarkable contribution of the higher-energy Y-shaped C2v isomer is also observed in the experimental spectrum. For Au4+·H2O, the most stable Cs (2A′) structure is formed through an AuO bond of H2O to the Au4+ (D2h) structure with a binding energy of 1.15eV. The Au4+·H2O structure exhibits Cs instead of C2v symmetry, which suggests substantial covalent contributions to the bonding between H2O and Au4+. The natural bond orbital charge analysis shows that a net positive charge of about 0.1e is transferred to H2O. The long-range corrected CAM-B3LYP* (ω=0.33) functional has proven reliable in predicting optical spectra of Au4+ and Au4+·H2O clusters close to experimental observation.