Flexible bonding between copper and nitric oxide: infrared photodissociation spectroscopy of copper nitrosyl cation complexes: [Cu(NO)n]+ (n = 1–5)

Abstract

The infrared spectra of mass-selected mononuclear copper nitrosyl cation complexes [Cu(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 experimental spectra provide distinctive patterns allowing the determination of the geometries and electronic structures of these complexes by comparison with the predicted spectra from density functional theory computations. The argon tagged [Cu(NO)₂Ar₂]⁺ and [Cu(NO)₃Ar]⁺ complexes as well as the higher n = 4 and 5 complexes each involve a bidentate (NO)₂ dimer ligand, suggesting that ligand–ligand coupling plays an important role in the bonding of these cation systems. The results also show that argon tagging has a strong influence on the geometric and electronic structures of the n = 2 and 3 complexes. The [Cu(NO)₄]⁺ cation is the most intense peak in the mass spectrum, which is characterized to be the fully coordinated ion with a D_2d structure involving two (NO)₂ units but with only 14-valence electrons on Cu. The [Cu(NO)₅]⁺ cation complex is determined to involve a [Cu(NO)₄]⁺ core ion that is coordinated by an external NO ligand.