The V+(NH3)n ions with n=4–8 are studied by infrared (IR) photodissociation spectroscopy in the NH-stretch region with the aid of density functional theory calculations. The calculations predict a square-planar coordination of V+ for the n=4 ion. In the IR spectra of n⩾5, red-shifted features emerge in the 3050–3300cm−1 region; overall spectral features agree well with those predicted for isomers with the square-planar coordination. A 6-coordinated isomer of n=6 is computed to be more stable than the square-planar structures, but the latter are actually observed in the experiment.