Spectroscopic confirmation of the tetrahedral geometry of tetraaquasilver(+) ion (Ag(H2O)4+)

Abstract

Ultraviolet absorption studies of aqueous solutions of the tosylate, sulfate, perchlorate, and tetrafluoroborate salts of Ag+ show that three bands at 225,210, and 192 nm are attributable to isolated Ag+ ions. These bands are believed to emanate from the parity-forbidden (4d95s) 'D -(4d'O) 'S excitation of Ag+, subject to ligand field effects of the primary hydration sphere. These bands have essentially temperature-independent oscillator strengths, which suggests that the static ligand field does not have a center of inversion. A tetrahedral arrangement of four water molecules in the primary hydration sphere, proposed earlier as a result of ESR studies, is consistent with these temperature-independent optical data. These same Ag+ bands appear (red shifted) in methanol solutions, which is again consistent with ESR studies showing a primary solvation sphere of four molecules and suggests that these molecules are arranged tetrahedrally. The absence of these bands in acetonitrile solutions corroborates the Dewar-Chatt bonding mechanism proposed to explain the preferential solvation of Ag+ by acetonitrile over water. The oscillator strength of the 225-nm band increases dramatically and linearly as the mole percent of ethanol in water/ethanol solvent is increased. These observations suggest that solvation of Ag+ by ethanol has a local symmetry that is less than tetrahedral and that the "preferential solvation" effect observed at 13 mol 70 ethanol by ESR is attributable to a polycrystalline glass transition. IntroductionThe ultraviolet spectrum of aqueous Ag+ has received very little attention, although the structure of the primary hydration shell of Ag+ has been studied intensively. This paper presents and characterizes the ultraviolet absorption bands of aqueous Ag+ at wavelengths >185 nm. The multiplet structure and the temperature dependence of the oscillator strength are interpreted in terms of ligand field effects as they relate to the symmetry of the primary hydration shell. A comparative study of this ultraviolet Ag+

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

“…In the C 3 H 8 -SCR condition without H 2 (spectrum (a)), no other absorption bands appeared, indicating that the Ag + ion is still predominant. The disappearance of the band at 235 nm may be due to the adsorption of NO x and/or H 2 O on the Ag + ion [56]. In the presence of 0.5% H 2 (spectrum (b)), new bands at 260 and 284 nm were observed.…”

“…In the presence of 0.5% H 2 (spectrum (b)), new bands at 260 and 284 nm were observed. According to the literature about various types of Ag clusters in rare gas solids, water, and zeolites [44,46,[48][49][50][51][52][53][54][55][56][57][58][59][60], the assignments of the UV-VIS bands of Ag species are summarized in table 1. Generally, Ag species with a larger number of Ag atoms give UV-VIS band at a higher wavelength.…”

Deep oxidation of methane over zirconia supported Ag catalysts

“…At high Ag exchange level, in addition to the absorption band at 220 nm, a strong band at 245 nm and a broad band at 450 nm are observed. The band at 220 nm is usually attributed to isolated Ag ions [45,47,48]. The absorption bands at 260, 340 and 400 nm are assigned to Ag d n clusters [45,51±53] observed in Ag-exchanged zeolites and inert gas matrices.…”

Untitled

“…The structure of the primary hydration shell of Ag + in aqueous solutions was investigated by neutron diffraction 11 and ultraviolet absorption. 12 There was good agreement on the primary hydration shell containing four water molecules. Investigation done by Antonio et al 13 provided some insights about the Ag + environment within the geltype membranes.…”