Cation-π interactions of Cu+

The cation-π interactions of Cu+ are systematically studied using the B3LYP/6-311+G(d,p) method. It is found that Cu+ could form a 6η cation-π complex with benzene. The binding energy of the benzene-Cu+ complex is calculated to be −48.7 kcal/mol, which is significantly higher than the binding energies of the benzene-Li+ (−36.0 kcal/mol), benzene-Na+ (−22.6 kcal/mol), and benzene-K+ (−15.3 kcal/mol) complexes. It is also found that the cation-centroid distances in the cation-benzene complexes correlate with the ionic radii of the diverse cations including Cu+, Li+, Na+, K+, Rb+, Cs+, Be2+, Mg2+, Ca2+, Ag+, Cr2+, Fe2+, and Ni2+. Electrostatic interaction is not found to be the major driving force for the cation-π complexation of Cu+. The major difference between the cation-π complexes of alkali cations and Cu+ is that Cu+ has strong 3d→πC6H6* back-bonding interactions. Cu+ can also form 6η cation-π complexes with a number of 1,3,5-tri-substituted benzenes such as C6H3(CN)3, C6H3F3, C6H3Cl3, C6H3(BH2)3, C6H3(CH3)3, and C6H3(SiH3)3. The electron-donating groups increase the binding energy whereas the electron-withdrawing groups reduce the binding energy. Nonetheless, in all of the cases the electrostatic interaction is not the major driving force for the cation-π complexes of Cu+. Finally, in the presence of counterions Cu+ tends to form 2η complexes with aromatic compounds. Thus there is probably no 6η cation-π complexes of Cu+ in the condense phase. The binding energies of the 2η complexes between benzene and CuX (X=F, Cl, Br, I, CN, and CH3) range from −11.3 to −25.6 kcal/mol. Therefore, the 2η-mode interaction between the aromatic compounds and Cu+ may have significant roles in many supramolecular systems.