Chemisorption-Induced 2D-3D-2D Structural Transitions in Gold Heptamer: (CO)nAu7- (n=1-4)

CO chemisorption onto the Au-7(-) cluster is investigated using photoelectron spectroscopy (PES) and ab initio calculations. It is found that CO binding can induce previously unreported 2D-3D-2D structural changes. The gold motif in the most stable structure of COAu7- is an intermediate between the two known stable 2D isomers of Au-7(-). Two minor isomers are observed in the PES of (CO)(2)Au-7(-); one is due to an unprecedented 3D Au-7(-) species with C-s symmetry. This 3D C-s Au-7 motif becomes a major isomer in (CO)(3)Au-7(-). The most stable isomers of COAu7- and (CO)(2)Au-7(-) are planar with identical Au-7 motifs; the stable planar isomers of (CO)(3)Au-7(-) include not only the global-minimum structure of Au-7(-) but also a planar hexagonal Au-7 motif. The PES spectrum of (CO)(4)Au-7(-) is markedly different, and its most stable structure consists of the global-minimum structure of Au-7(-), three terminal CO, and one bridging CO.