title: Infrared spectroscopy of gas-phase Cr+ coordination complexes: determination of binding sites and electronic states.
abstract: Infrared spectra were recorded for a series of gas-phase Cr+ complexes using infrared multiphoton dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The functionalized aromatic ligands (acetophenone, anisole, aniline, and dimethyl aniline) offer a choice of either aromatic ring-pi or n-donor-base binding sites. Use of the FELIX free electron laser light source allowed convenient, rapid scanning of the chemically informative wavelength range from approximately 500 to 1800 cm(-1), which in many cases characterized the preferred site of metal binding, as well as the electronic spin state of the complex. Mono-complex ions, Cr+(ligand), for anisole, aniline, and dimethyl aniline and bis-complex ions, Cr+(ligand)(2), for anisole, aniline, and acetophenone were produced by ligand attachment to laser-desorbed Cr+ ions in the FT-ICR cell. The photodissociation yields plotted as a function of wavelength were interpreted as approximations to the infrared absorption spectra and were compared with computed spectra of different possible geometries and spin states. Clear-cut diagnostic features in the spectra of the acetophenone, anisole, and aniline complexes showed the sites of Cr+ attachment to be the carbonyl oxygen site for acetophenone (bis-complex) and the ring-pi site for anisole and aniline (both mono- and bis-complexes). The bis-complexes of aniline and anisole are low-spin (probably doublet) states, while the mono-complexes of these same ligands are high-spin (sextet) states. The dimethyl aniline complex gave a cluttered spectrum in poor agreement with calculations, which may reflect a mixture of binding-site isomers in this case.
authors.affiliation: FOM Institute for Plasma Physics "Rijnhuizen", Postbus 1207, 3430 BE Nieuwegein, The Netherlands.
authors.forename: David T
authors.initials: DT
authors.lastname: Moore
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.forename: John R
authors.initials: JR
authors.lastname: Eyler
authors.forename: Gert
authors.initials: G
authors.lastname: von Helden
authors.forename: Gerard
authors.initials: G
authors.lastname: Meijer
authors.forename: Robert C
authors.initials: RC
authors.lastname: Dunbar