In the IR-spectra, the sharp peaks at 2115 cm -1 for 1 + TfO -and 2131 cm -1 for 2 + TfO -were assigned to the symmetric C≡C stretching vibration, which is in good agreement with the calculated values 2150 cm -1 and 2161 cm -1 , respectively, simulated at the B3LYP-D3/6-31G** level with a scaling factor of 0.9648. These values fall within the standard range (2260-2100 cm -1 ) for the symmetric C≡C stretching vibration, but the relatively small values indicate the slight contribution of a canonical butatriene structure.