Observation of linear to planar structural transition in sulfur-doped gold clusters: AuxS- (x=2-5)

We report a joint experimental and theoretical study on the structures of a series of gold clusters doped with a sulfur atom, AuxS- (x = 2-5). Well-resolved photoelectron spectra are obtained and compared with theoretical results calculated using several density functional methods to elucidate the structures and bonding of AuxS- (x = 2-5). Au2S- is found to have an asymmetric linear global minimum structure with C-infinity v symmetry, while the most stable structure of neutral Au2S is bent with C-2v symmetry, reminiscent of H2S. Au3S- is found to have an asymmetric bent structure with an Au-S-Au-Au connectivity. Two isomers are observed experimentally to co-exist for Au4S- : a symmetric bent 1D structure (C-2v) and a 2D planar low-lying isomer (C-s). The global minimum of Au5S- is found to be a highly stable planar triangular structure (C-2v). Thus, a 1D-to-2D structural transition is observed in the AuxS- clusters as a function of x at x = 4. Molecular orbital analyses are carried out to obtain insight into the nature of the chemical bonding in the S-doped gold clusters. Strong covalent bonding between S and Au is found to be responsible for the 1D structures of AuxS- (x = 2-4), whereas delocalized Au-Au interactions favor the 2D planar structure for the larger Au5S- cluster. (C) 2013 AIP Publishing LLC.