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

Trystan Bennett, Alexander Falcinella, Reuben White, Rohul Adnan, Vladimir Golovko, Gunther Andersson, Gregory Metha

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    1 Citation (Scopus)

    Abstract

    Two tris(triphenylphosphinegold)oxonium dimer salts [{{Au(PPh3)}33-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(PPh3)}33-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(PPh3)}33-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(PPh3)}33-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(PPh3)}33-O)}2]2+(BF-4)2 and [{{Au(PPh3)}33-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.

    Original languageEnglish
    Pages (from-to)74499-74505
    Number of pages7
    JournalRSC Advances
    Volume5
    Issue number91
    DOIs
    Publication statusPublished - 2015

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