Covalent gold

Abstract

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)).

Periodicity and Covalency of [MX2]– (M = Cu, Ag, Au, Rg; X = H, Cl, CN) Complexes

“…[4b, 11,23] The AuH 2 -complex is an interesting model system to explore this similarity. In this work we compared the energy levels of a series of linear Au n H 3-n -(n = 0, 1, 2, 3) complexes, as shown in Figure 9.…”

Explaining the magnetism of gold

“…Taking into account the relativistic contraction, the 6s and 5d orbitals are closer, and a s-d hybridizations is feasible [11]. For convenience, Au 2 will be considered, in the proposed molecular orbital diagram shown in Figure 3 The molecular orbital diagram in Figure 1 explains the diamagnetism of bulky gold, whereas the diagram in Figure 3 explains the paramagnetism of gas phase Au 2 (and, by extension, the paramagnetism of gold clusters and nanoparticles).…”

Investigation into the metallophilic interaction in coinage-metal halides: an ab initio study of CMX (CM = Cu and Ag, X = F − I)

“…CMs show very rich chemistry with relatively strong relativistic effects, which decreases considerably the size of the valence s orbital and leads to the expansion of the inner d orbital [4,5]. Interactions with obvious covalent character are increasingly being found in CM-containing compounds [6]. In studying the very weak interactions between CM and the atoms of noble gases, our previous results indicate clearly that there is considerable covalent character in the Cu-Xe interaction [7,8].…”