Ab initiomolecular-orbital study of structures and energetics of Si3H3 neutral and anion

Covalent gold

Gold is known to be the noblest of all metals because of the relativistic stabilization of its outer 6s orbital. The relativistic effects also lead to destabilization of the 5d orbitals, reducing the 6s-5d energy gap and enhancing s-d hybridization. Therefore, in contrast to its lighter congeners, gold exhibits significant covalent bonding characters and a remarkable repertoire of chemistry, which are increasingly being exploited in catalysis and nanotechnology. This Perspective presents a brief account of recent experimental efforts in the author's laboratory using photoelectron spectroscopy that lead to direct observations of covalent bonding in several relatively simple Au compounds: Au oxides (AuO(-) and AuO(2)(-)), sulfides (AuS(-) and AuS(2)(-)), and the well-known Au(CN)(2)(-) complex. In a series of Au-Si and Au-B mixed clusters, it has also been found that gold atoms behave like H atoms, forming auro-silicon and auro-boron clusters with strong covalent bonding, analogous to the corresponding silicon and boron hydrides, such as the tetrahedral auro-silane (SiAu(4)) versus silane (SiH(4)).

Gold as hydrogen: Structural and electronic properties and chemical bonding in Si3Au3+∕0∕− and comparisons to Si3H3+∕0∕−

A single Au atom has been shown to behave like H in its bonding to Si in several mono- and disilicon gold clusters. In the current work, we investigate the AuH analogy in trisilicon gold clusters, Si3Au3(+0-). Photoelectron spectroscopy and density functional calculations are combined to examine the geometric and electronic structure of Si3Au3-. We find that there are three isomers competing for the ground state of Si3Au3- as is the case for Si3H3-. Extensive structural searches show that the potential energy surfaces of the trisilicon gold clusters (Si3Au3-, Si3Au3, and Si3Au3+) are similar to those of the corresponding silicon hydrides. The lowest energy isomers for Si3Au3- and Si3Au3 are structurally similar to a Si3Au four-membered ring serving as a common structural motif. For Si3Au3+, the 2pi aromatic cyclotrisilenylium auride ion, analogous to the aromatic cyclotrisilenylium ion (Si3H3+), is the most stable species. Comparison of the structures and chemical bonding between Si3Au3(+0-) and the corresponding silicon hydrides further extends the isolobal analogy between Au and H.