BDEtheor [kJ mol ] BDEexp [kJ mol ] BDEtheor [kJ mol We have also studied BDEs for the complexes with the tridentate ligand terpy and X = Cl and Br. The results show that the terpy ligand reduces the binding energies of the halogens in the gold(III) complexes [(terpy)Au III X2] + by more than 60 kJ mol -1 . The reason probably stems from the assistance of one of the pyridine units in the elimination of the halogen radical (see Figure ). The binding energies of the halogen atoms in the gold(II) complexes [(terpy)Au II X] + remain very close to those in [(bipy)Au II X] + . We also investigated the formation of the dicationic gold(II) complexes from the [(terpy)Au III X] 2+ precursors (the bottom of Table ). The results show that the energy required for the formation of [(terpy)Au II ] 2+ is only slightly smaller than that for the formation of the gold(II) complexes with the bipy ligand.