Coordination and solvation of copper ion:: infrared photodissociation spectroscopy of Cu+ (NH3)n (n=3-8)

Coordination and solvation structures of the Cu+( NH3)(n) ions with n = 3 - 8 are studied by infrared photodissociation spectroscopy in the NH- stretch region with the aid of density functional theory calculations. Hydrogen bonding between NH3 molecules is absent for n = 3, indicating that all NH3 molecules are bonded directly to Cu+ in a tri- coordinated form. The. rst sign of hydrogen bonding is detected at n = 4 through frequency reduction and intensity enhancement of the infrared transitions, implying that at least one NH3 molecule is placed in the second solvation shell. The spectra of n = 4 and 5 suggest the coexistence of multiple isomers, which have different coordination numbers ( 2, 3, and 4) or different types of hydrogen- bonding con. gurations. With increasing n, however, the di- coordinated isomer is of growing importance until becoming predominant at n = 8. These results signify a strong tendency of Cu+ to adopt the twofold linear coordination, as in the case of Cu+( H2O) (n).