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

摘要

Two tris(triphenylphosphinegold) oxonium dimer salts [{{Au(PPh3)}(3)(mu(3)-O)}(2)](2+)(X-)(2) (X = BF4- , MnO4- 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)}(3)(mu(3)-O)}(2)](2+)(BF4-)(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)}(3)(mu(3)-O)}(2)](2+)(BF4-)(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)}(3)(mu O3-)}(2)](2+)(MnO4- spectrum but is masked by experimental noise. In the 50400 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)}(3)(mu(3)-O)}(2)](2+)(BF4-)(2) and [{{Au(PPh3)}(3)(mu(3)-O)}(2)](2+)(MnO4-)(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.