Infrared spectra of mass-selected mononuclear iron nitrosyl cations Fe(NO)(n)(+) with n = 1-5 and their argon tagged complexes are measured via infrared photodissociation spectroscopy in the nitrosyl stretching frequency region in the gas phase. The structures are established by comparison of the experimental spectra with the simulated spectra derived from density functional calculations. Two IR active bands were observed for the argon-tagged Fe(NO)(2)(+) and Fe(NO)(3)(+) complexes, consistent with theoretical predictions that these complexes have bent C-2v and nonplanar C-3v symmetry, respectively. The Fe(NO)(4)(+) complex was characterized to have a completed coordination sphere with 17 electrons containing a bent one-electron NO ligand and three three-electron NO ligands. The Fe(NO)(5)(+) complex was determined to involve a Fe(NO)(4)(+) core ion that is solvated by an external NO molecule.