Evidence for Emergent Chemical Bonding in Au⁺−Rg Complexes (Rg = Ne, Ar, Kr, and Xe)

Abstract

Evidence is presented that there is a clear covalent component in the bonding of Au+ to Kr and Au+ to Xe, with some evidence that there may be such bonding between Au+ and Ar; for Au+ and Ne, there is no such evidence, and the bonding seems to be entirely physical. A model potential analysis shows that when all attractive inductive and dispersive terms out to R-8 are properly included in the Au+-Ne case, with an Ae(-bR) Born-Mayer repulsive term, essentially all the bonding in Au+-Ne can be rationalized by physical attraction alone. This is consistent with a natural bond order (NBO) analysis of the Au+-Ne ab initio wavefunctions, which shows the charge on Au+ to be very close to 1.0. In contrast, similar model potential and NBO analyses show quite clearly that physical interactions alone cannot account for the large bond energy values for the Au+-Kr and Au+-Xe complexes and are consistent with covalent contributions to the Au+-Kr and Au+-Xe interactions. Au+-Ar is seen to lie on the borderline between these two limits. In performing the model potential analyses, high-level ab initio calculations are employed [CCSD(T) energies, extrapolated to the complete basis set limit], to obtain reliable values of Re, De and omegae as input. A comparison of the gold-Xe bond distances in several solid-state Au(I, II and III) oxidation-state complex ions, containing "ligand" Xe atoms, prepared by Seppelt and co-workers, with that of the "free" Au+-Xe gas-phase ion is made, and a discussion of the trends is presented.

Theory meets experiment: Gas-phase chemistry of coinage metals

“…Shortly afterwards, these gas-phase studies were followed by the isolation of the first gold-xenon compound in the condensed phase [72], and also triatomic XeAuF has been detected in the gas phase via microwave rotational spectroscopy [73]. Most recently, the binding patterns of AuXe + and related gold/rare-gas compounds have been analyzed in detail by Belpassi et al [74] who quantified the significant amount of charge transfer in these compounds by means of relativistic four-component calculations [75]. Also the CuXe + cation has been observed experimentally, which has a significant binding energy of D(Cu + -Xe) = 98 kJ mol −1 [76], whereas the silver analog AgXe + could not be generated under similar conditions [18,77], suggesting that D(Ag + -Xe) is much lower than D(Cu + -Xe) and D(Au + -Xe).…”

Theoretical treatment of (M=Cu, Ag and Au)

“…Noble gas (Ng) chemistry has turned into a new and fascinating field of study since the Ng-containing compound, xenon hexafluoroplatinate [Xe þ (PtF 6 ) À ], was reported four decades ago [1]. In particular, species containing both inert noble gases and noble metal atoms have stimulated great interest.…”

“…In particular, species containing both inert noble gases and noble metal atoms have stimulated great interest. Ng-M bonding in the complexes NgMX(Ng¼Ar, Kr, Xe; M¼Cu, Ag, Au; and X¼F, Cl, Br) has been the subject of many theoretical and experimental studies [2][3][4][5][6][7][8]. Recently, Seidel and Seppelt [9] demonstrated the existence of the [AuXe 4 ] 2þ cation in the crystal structure of AuXe 2þ 4 Sb 2 F À1 11 À Á 2 ; in the complex, Xe functions as an electron donor to Au 2þ .…”

Theoretical investigation of stabilities and interactions of AuNenZ(n= 1–3,Z= −1, 0, +1) clusters

“…Pyykko¨ [3] suggested that most of the bonding is covalent in character, but this interpretation was questioned by Read and Buckingham, who noted that 'covalency within the RgAu þ species appears to be unproven' [5]. Recent investigations [26,29] show that there is clearly a covalent component in the bonding of Xe(Kr/Ar)-Au þ . However, the heavier rare gases, xenon or krypton, have more varied chemistry than the lighter one, neon, due to their greater polarizability.…”