CCSD(T) and MRMP calculations with TZP + quality basis sets are used to study the interaction of Cu2+ with up to two ligand molecules L (L = H2O, H2S, NH3, and PH3). The dissociation to Cu+ and L+ is much more stable than the formation of Cu2+ L adducts (by 76-100 kcal/mol). Nevertheless, it might be possible to obtain a one-ligand complex for H2O and NH3; barrier heights of 7 and 9 kcal/mol, respectively, are assigned for the dissociation process, Two ligands from H2O and NH3 can give more stable complexes with Cu2+ as the barrier heights reach 40 kcal/mol. In order to obtain stable complexes of PH3 or H2S with Cu2+, at least two ligands are required.