title: Gas-phase IR spectroscopy of anionic iron carbonyl clusters.
abstract: The first gas-phase vibrational spectra are presented for several anionic iron carbonyl clusters, ranging in size from Fe(CO)4- to Fe5(CO)14- in the CO-stretching region (1600-2100 cm-1). The experimental spectra provide some immediate structural information about the clusters in the form of low-wavenumber (1750-1850 cm-1) bands marking the presence of bridging carbonyl ligands (mu2-COs). Supporting DFT calculations are presented for the smaller clusters (<3 Fe atoms) and give good agreement with the experimental data, allowing structural assignments for these cases. The Fe2(CO)7- spectrum suggests a structure lacking bridging carbonyl ligands, in agreement with the DFT results. For the case of Fe2(CO)8-, there are two possible structures based on the calculations, both with and without bridging carbonyls. The presence of a low-frequency band ( approximately 1770 cm-1) in the experimental spectrum conclusively demonstrates the existence of the bridged form. The ramifications of these data for metal-metal bonding in the clusters are also considered.
authors.affiliation: FOM Institute for Plasma Physics "Rijnhuizen", Edisonbaan 14, 3439 MN Nieuwegein, The Netherlands. dtmoore@rijnh.nl
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: Gerard
authors.initials: G
authors.lastname: Meijer
authors.forename: Gert
authors.initials: G
authors.lastname: von Helden
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Ridge