Coordination and Solvation of the Au⁺ Cation: Infrared Photodissociation Spectroscopy of Mass-Selected Au(H₂O)_n⁺ (n = 1–8) Complexes

Abstract

Gold cation-water complexes with attached argon atoms are produced via a laser vaporization supersonic cluster source. The [Au(H(2)O)(n)Ar(x)](+) (n = 1-8; x = 1 or 2) complexes are each mass selected and studied by infrared photodissociation spectroscopy in the OH stretching frequency region to explore the coordination and solvation structures of the Au(+) cation. Density functional calculations have been performed, and the calculated vibrational spectra are compared to the experimental spectra to identify the gas-phase structures of the Au(H(2)O)(n)(+) complexes. Confirming previous theoretical predications, the first coordination shell of the Au(+) cation contains two water molecules forming a linear O-Au(+)-O arrangement; subsequent water molecules bind to the two H(2)O ligands of the Au(H(2)O)(2)(+) core ion via hydrogen bond forming of the second hydration shell, which is complete at n = 6. For the complexes with n ≤ 7, the experimental spectrum can in general be assigned to the predicted global minimum structure. However, the spectrum suggests that two or more conformers coexist for the n = 8 complex, indicating that the identification of a single global minimum becomes less important upon increasing the number of solvating water molecules.

Microsolvation of Zn cations: infrared multiple photon dissociation spectroscopy of Zn+(H2O)n (n = 2–35)

“…72 The most red-shifted band is also present for clusters n 4 4, centred at 3220 cm À1 for n = 7, and even in the largest cluster with n = 35, a slightly blue-shifted maximum at 3230 cm À1 can be identified in an overall broad absorption band that is typical for water clusters. The shift to the red, as outlined in many previous publications, 3,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][73][74][75] is due to the metal-induced polarisation on the water molecules, which removes electron density from bonding orbitals on the O-H bond, causing an observed red-shift. As discussed previously for Zn + (H 2 O) n complexes, 43 the polarizing effect of Zn + , when compared to other singly-charged metal ions, 3,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][73][74]…”

Infrared Study of OCS Binding and Size-Selective Reactivity with Gold Clusters, Aun+ (n = 1–10)

“…67 Infrared action spectroscopy has also been used extensively to study Au + -Lm (L = N2O, CO, NO, H2O, and small hydrocarbons) metal-ligand complexes. [74][75][76][77][78][79] When radical species such as OH are preadsorbed onto gold cluster anions the odd-even pattern in cluster reactivity reverses, accounting for the role of water in the enhanced activity of some nano gold catalysts. 12 Indeed, the binding of one molecule to a cluster can have a profound effect on the subsequent adsorption of a second molecule.…”

Near ultraviolet photodissociation spectroscopy of Mn+(H2O) and Mn+(D2O)

“…Likewise, Nishi and co-workers measured vibrational spectra of M + (H 2 O) n for M = V, 23 Co, 24 Cu and Ag, 25 while Zhou and co-workers measured the vibrational spectra of Au + (H 2 O) n (n = 1-8). 26 In addition, van der Linde and Beyer have examined water activation in larger clusters of M + (H 2 O) n (n < 40) (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in a FT-ICR mass spectrometer, with particular emphasis on water activation in Mn + (H 2 O) n . 27 O Brien and Williams used vibrational spectroscopy to observe similar effects in smaller divalent clusters (n = 5-8).…”