The effect of counter ions on the far-infrared spectra of tris(triphenylphosphinegold)oxonium dimer salts

Abstract

Two tris(triphenylphosphinegold)oxonium dimer salts [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (X À ) 2 (X ¼ BF À 4 , MnO À 4 ) were investigated via synchrotron-based far-infrared vibrational spectroscopy and density functional theory modelled at the M06/LANL2DZ level of theory. The 50-800 cm À1 region of both oxonium salts is presented, with the spectrum for [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (BF À 4 ) 2 found to possess a large feature at 330.3 cm À1 , attributable to counter-ion vibrational modes, which is only predicted upon explicit inclusion of counter-ions in the calculation. A feature around 107 cm À1 observed for the [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (BF À 4 ) 2 infrared spectrum is assigned to 21 distinct vibrational modes arising from Au-Au bond stretching and other motions of the Au core. The same feature is predicted to be present within the [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (MnO À 4 ) 2 spectrum but is masked by experimental noise. In the 50-400 cm À1 region, the relative intensities of predicted vibrational modes is found to depend heavily on the presence and nature of the counter-ions, while within the 400-800 cm À1 region, little dependence of the theoretical spectra on the type of counter-ion is predicted. Finally, the dimerization energies of both [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (BF À 4 ) 2 and [{{Au(PPh 3 )} 3 (m 3 ÀO)} 2 ] 2+ (MnO À 4 ) 2 are calculated to be 3.06 eV and 3.20 eV, respectively, when the counter-ions are explicitly included within the calculation, and just 1.10 eV in their absence.

Revisiting ultrasmall phosphine-stabilized rhodium-doped gold clusters AunRh (n = 5, 6, 7, 8): geometric, electronic, and vibrational properties

“…19 Metal core motion and ligand suppression can be analyzed using infrared spectroscopy by detecting the vibrational modes of key functional groups. Several studies have reported the IR spectra of ligand-stabilized gold clusters, [20][21][22][23] but we are not aware of any involving the Au n Rh clusters. This present work extends our previous far-IR and computational studies of atomically precise gold-based clusters 20,21 and ruthenium-based clusters 24 to ligand-protected bimetallic Au n Rh clusters (n = 5-8) focused on low frequency vibrational modes (l = 50-450 cm À1 ).…”

Aggregation Behavior of Ligand-Protected Au9 Clusters on Sputtered Atomic Layer Deposition TiO2

“…Gold nanoclusters (Au NCs) are smaller in size than Au NPs and are used to modify surface properties as well. In contrast to nanoparticles, it is not the crystal structure but the geometric fluxionality and the size dependence of the electronic structure that are important for surface modification by clusters. − Au NCs form specific atomic structures depending on the number of atoms forming the NCs, while Au NPs typically adopt a face-centered cubic (fcc) structure. , Au NCs, like molecules, have discrete electronic energy levels, while NPs have a continuous electronic energy band structure similar to that of bulk Au. , For this reason, the number of atoms forming a Au NC strongly influences the properties of NC modified surfaces. − One example is the catalytic properties of surfaces modified with Au NCs, which depend on the size, morphology and electronic structure of the Au NCs. − The catalytic properties of cluster-modified surfaces change with the size of Au NCs, and the size of the NCs needs to be preserved to retain specific surface properties . Agglomeration of NCs leads to an increase in NC size, eventually forming NPs, and should be avoided.…”