Infrared photodissociation spectra and solvation structures of Cu⁺(H₂O)_n (n = 1-4)

Coordination and solvation structures of the Cu⁺(H₂O)_n ions with n = 1-4 are studied by infrared photodissociation spectroscopy and density functional theory calculations. Hydrogen-bonding between H₂O molecules is detected in Cu⁺(H₂O)₃ and Cu⁺(H₂O)₄ through a characteristic change in the position and intensity of OH-stretching transitions. The third and fourth waters prefer hydrogen-bonding sites in the second solvation shell rather than direct coordination to Cu⁺. The infrared spectroscopy verifies that the gas-phase coordination number of Cu⁺ in Cu⁺(H₂O)_n is two and the resulting linearly coordinated structure acts as the core of further solvation processes.