The effect of counter ions on the far-infrared spectra of tris(triphenylphosphinegold)oxonium dimer saltsElectronic supplementary information (ESI) available: Containing a comparison between the crystallographic and DFT-optimized Au6O2 core, optimized structures for the [[(Ph3PAu)3O]BF4]2 and [[(Ph3PAu)3O]MnO4]2 species, and a comparison between the theoretical spectra for the [(PPh3Au)3O]− and ([(PPh3Au)3O]−)2 species. See DOI: 10.1039/c5ra11599j

• Main Authors: Bennett, Trystan, Falcinella, Alexander J, White, Reuben J, Adnan, Rohul H, Golovko, Vladimir, Andersson, Gunther G, Metha, Gregory F
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c5ra11599j

Two tris(triphenylphosphinegold)oxonium dimer salts [{{Au(PPh 3 )} 3 (μ 3 −O)} 2 ] 2+ (X − ) 2 (X = BF − 4 , MnO − 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 −1 region of both oxonium salts is presented, with the spectrum for [{{Au(PPh 3 )} 3 (μ 3 −O)} 2 ] 2+ (BF − 4 ) 2 found to possess a large feature at 330.3 cm −1 , attributable to counter-ion vibrational modes, which is only predicted upon explicit inclusion of counter-ions in the calculation. A feature around 107 cm −1 observed for the [{{Au(PPh 3 )} 3 (μ 3 −O)} 2 ] 2+ (BF − 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 (μ 3 −O)} 2 ] 2+ (MnO − 4 ) 2 spectrum but is masked by experimental noise. In the 50-400 cm −1 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 −1 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 (μ 3 −O)} 2 ] 2+ (BF − 4 ) 2 and [{{Au(PPh 3 )} 3 (μ 3 −O)} 2 ] 2+ (MnO − 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. The far-infrared spectra of two tris(triphenylphosphinegold)oxonium dimer salts in the 50-800 cm −1 region were recorded using synchrotron-based IR radiation, and comprehensively assigned utilising density functional theory calculations.