Infrared photodissociation spectroscopy of V⁺(H₂O)_n (n = 2-8): Coordinative saturation of V⁺ with four H₂O molecules

The V⁺(H₂O)_n ions with n = 2-8 are studied by infrared (IR) photodissociation spectroscopy. The IR spectra indicate that H₂O molecules are allowed to bind directly to V⁺ until the completion of a 4-coordinated structure and additional molecules are forced to occupy outer solvation shells. Density functional theory calculations suggest that one empty orbital in V⁺ (3d⁴) before coordination can be identified with the 3 d_{x2 - y2} orbital, which provides four sites of lower electron density along the x and y axes. This results in a strong interaction with only four H₂O molecules, and thus, a stable square-planar V⁺(H₂O)₄ complex.