Next, we investigated spectroscopic properties of the [(bipy)Au II X] + complexes (X = Cl and Br) in the gas phase and compared them with the analogous complexes of copper(II). 2,2'-Bipyridine is usually not considered as a redox-active ligand. However, a C-H bond of 2,2'-Bipyridine can be activated by several metals in a roll-over mechanism. Further, strongly redox-active metals can affect the structure of the bipyridine ligand. We have assumed that if the C-H activation reactivity or the redox reactivity would be important for the gold(II) complexes, then we should detect distinct signatures by vibrational and electronic spectroscopy of the mass-selected complexes. For an easier interpretation, we compared all spectral features with those of analogous copper complexes. We measured IR spectra by helium tagging photodissociation method. In the range of our OPO IR light source, the spectra show mostly only the vibrations of the bipy ligand (Figure ). The comparison of gold and copper (M = Au or Cu) analogs of [(bipy)M II Cl] + and [(bipy)M II Br] + reveals that both metals interact with the ligand in the same way (compare the top IRPD spectra in both columns in Figure ). The spectra do not reveal any significant differences. We also measured IR spectra of the gold(III) precursors (bottom IRPD spectra in Figure ). The gold(III) complexes show a very similar fingerprint of the bipy ligands as the respective gold(II) complexes. The comparison of the experimental spectra with the IR spectra predicted by DFT (B3LYP-D3BJ -the most frequently used functional in ion spectroscopy -in grey in Figure ) shows a very good agreement. The agreement suggests that the DFT method describes well the interaction between gold(II) and the ligand as well as the overall geometry of the complex 2.5 Electronic photodissociation spectra Next, we have characterized the newly prepared gold(II) complexes [(bipy)Au II X] + (X = Cl or Br) by measuring their absorption spectra in the visible range using the helium tagging photodissociation method. For the comparison, we measured also the spectra of the stable copper(II) analogs [(bipy)Cu II Cl] + and [(bipy)Cu II Br] + . The copper chlorido complex has an absorption band below 450 nm. We could detect only the onset of this band, because of the working range of our laser (Figure ). The absorption maximum for [(bipy)Cu II Br] + is red shifted to 544 nm (Figure ). For the gold complexes, we detect a band at 637 nm for [(bipy)Au II Cl] + (Figure ) and two bands at 494 nm and 663 nm for [(bipy)Au II Br] + (Figure ). In order to explain the spectra and get a deeper insight into the properties of gold(II) complexes, we have performed quantum chemical calculations.