Knowing the ligands that can stabilize gold(II) halido complexes, we have attempted to prepare the respective gold(II) complexes also in solution by electrochemical reduction. Unfortunately, the electrochemical reaction led always to the twoelectron reduction and the formation of gold(I) complexes. Nevertheless, we have observed the trend in the onset potential for the reduction of the gold(III) complexes that correlates well with the gas-phase halogen bond dissociation energies from the respective [(L)Au III X2] + ions (Figure ). For the tridentate ligand terpy, the reduction is reversible. We assume that the complex is mostly present as [(terpy)Au III X] 2+ which has the favourable square planar geometry and also represents the dominant complex detected by electrospray ionization mass spectrometry (Figure & S29). The [(terpy)Au III X] 2+ complexes can accept 2 electrons without forming an unstable species (Reaction 5 in Figure ). On contrary, the bidentate ligand will support the [(bipy)Au III X2] + speciation. Electrochemical reduction of these complexes was always irreversible. Likely, the [(bipy)Au III X2] + complexes accept 2 electrons and then spontaneously dissociate to form linear [AuX2]¯ and the free ligand. Interestingly, a rough correlation between the BDEs of the halogen atoms in [(L)Au III X2] + and the reduction onset potentials (blue points in Figure ) suggests that the energy of the gas-phase homolytic M-X bond cleavage can to a certain degree predict the redox potential of the metal M. The possibility to generate the gold(II) halido complexes in the gas phase allowed us to characterize their spectroscopic properties. Using infrared photodissociation spectroscopy, we could show that gold(II) has a very similar electronic interaction with the auxiliary ligands as copper(II). The IR spectra showing the vibrations of bipy ligand do not suggest any unpaired electron delocalization at the ligand. The gold(II) complexes absorb also in the visible range. In comparison to the analogous copper(II) complexes, their absorption maxima are slightly blue shifted. The spectra suggest the orange-red color for [(bipy)Au II Br] + and cyan for [(bipy)Au II Cl] + . The theoretical analysis of the spectra showed that the excitations are metal-centered and also demonstrated how subtle structural variations and vibronic coupling dramatically change the intensities of peaks and also shift non-negligibly the positions of the absorption peaks. QTAIM calculations confirm that both gold and copper are in oxidation state M II in calculated [(bipy)M II X] + systems, with the calculated M-X bond order between 1 and 1.5 (multiple bonding) and with the M-N bond orders near 0.7 (dative bonding). The NBO analysis reveals a strong interaction of the in-plane LP(X) with the empty d orbital at the gold(II) center.