All‐Metal Clusters that Mimic the Chemistry of Halogens

Abstract

Owing to their s(2)p(5) electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH(4), mimic the chemistry of halogens and readily form salts (e.g., Na(+)(AlH(4))(-)), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage-metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX(4) (X=Cu, Ag, Au), these metal atoms may exhibit halogen-like properties. By using density functional theory, we show that AlAu(4) not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu(4))(2)(-) (M=Na and K) and anionic (FAuF)Au(FAuF) range from 4.06 to 5.70 eV. Au-based superhalogen anions, such as AlAu(4)(-) and AuF(2)(-), have the additional advantage that they exhibit wider optical absorption ranges than their H-based analogues, AlH(4)(-) and HF(2)(-). Because of the catalytic properties and the biocompatibility of Au, Au-based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu(4), AlX(4) (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom.

Network Formation by Condensed Tetrahedral [Au3Al] Units in Na2Au3Al: Crystal and Electronic Structure, Spectroscopic Investigations, and Physical Properties of an Ordered Ternary Auride

“…As for the binary Na−Al system, no experimental data is available; however, numerous papers have been published that predict various clusters (e.g., NaAl 7 ). 41 For the ternary system, thus far, only theoretical calculations have been reported, including the optical properties of A 2 AuAl (A = Li−K), 42 the ability of [AlAu 4 ] clusters to mimic halogens, 43 and the structural and optical properties of naked and passivated [Au 5 Al 5 ] nanoclusters. 44 Here, we report the synthesis, physical, and structural characterization of Na 2 Au 3 Al, the first compound in the ternary Na−Au−Al system, and of the solid solution Na 2 Au 4−x Al x (x = 0−1).…”

Signature of Au as a Halogen

“…For example, the photoelectron spectra of Au n F m – and Au n +1 F m –1 – should exhibit analogous patterns. Another signature of Au behaving as a halogen would be to show experimentally that it can serve as the building block of a superhalogen. , For example, can the EA of Au 2 F exceed that of F?…”

“…Gagliardi and Pyykko 13 later observed a transition from halogen-like to hydrogen-like chemical behavior of MAu 6 species (M = Cr, Mo, or W). The fact that Au, like halogens, can form superhalogens was demonstrated by Zhao et al, 14 who calculated the vertical detachment energy (VDE) of AlAu 4 to be 3.98 eV. However, to the best of our knowledge, no direct experimental evidence of Au behaving as a halogen in small clusters exists.…”

18-Electron rule inspired Zintl-like ions composed of all transition metals

“…Since H and Au are isovalent and previous studies have demonstrated that Au can mimic the properties of H in compounds, 41 we explored whether [FeAu 6 ] 4À could behave like a Zintl-like ion and if so can a crystal of Mg 2 (FeAu 6 ) be stabilized with Fm% 3m symmetry. We optimized the crystal structure of Mg 2 (FeAu 6 ) and found that it retains its Fm% 3m symmetry (Fig.…”