title: Infrared multiple photon dissociation spectroscopy of a gas-phase oxo-molybdenum complex with 1,2-dithiolene ligands.
abstract: Electrospray ionization (ESI) in the negative ion mode was used to create anionic, gas-phase oxo-molybdenum complexes with dithiolene ligands. By varying ESI and ion transfer conditions, both doubly and singly charged forms of the complex, with identical formulas, could be observed. Collision-induced dissociation (CID) of the dianion generated exclusively the monoanion, while fragmentation of the monoanion involved decomposition of the dithiolene ligands. The intrinsic structure of the monoanion and the dianion were determined by using wavelength-selective infrared multiple-photon dissociation (IRMPD) spectroscopy and density functional theory calculations. The IRMPD spectrum for the dianion exhibits absorptions that can be assigned to (ligand) C ═ C, C-S, C-C ≡ N, and Mo ═ O stretches. Comparison of the IRMPD spectrum to spectra predicted for various possible conformations allows assignment of a pseudo square pyramidal structure with C2v symmetry, equatorial coordination of MoO(2+) by the S atoms of the dithiolene ligands, and a singlet spin state. A single absorption was observed for the oxidized complex. When the same scaling factor employed for the dianion is used for the oxidized version, theoretical spectra suggest that the absorption is the Mo ═ O stretch for a distorted square pyramidal structure and doublet spin state. A predicted change in conformation upon oxidation of the dianion is consistent with a proposed bonding scheme for the bent-metallocene dithiolene compounds [Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976 , 98 , 1729 - 1742], where a large folding of the dithiolene moiety along the S · · · S vector is dependent on the occupancy of the in-plane metal d-orbital.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University , 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: van Stipdonk
authors.forename: Partha
authors.initials: P
authors.lastname: Basu
authors.forename: Sara A
authors.initials: SA
authors.lastname: Dille
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
mesh_terms: D005740:Gases / Q000737:chemistry; D008024:Ligands; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D017785:Photons; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D005740:Gases; D008024:Ligands; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D008982:Molybdenum; D010100:Oxygen