title: Infrared multiphoton dissociation spectroscopy of a gas-phase complex of uranyl and 3-oxa-glutaramide: an extreme red-shift of the [O═U═O](2+) asymmetric stretch.
abstract: The gas-phase complex UO2(TMOGA)2(2+) (TMOGA = tetramethyl-3-oxa-glutaramide) prepared by electrospray ionization was characterized by infrared multiphoton dissociation (IRMPD) spectroscopy. The IRMPD spectrum from 700-1800 cm(-1) was interpreted using a computational study based on density functional theory. The predicted vibrational frequencies are in good agreement with the measured values, with an average deviation of only 8 cm(-1) (<1%) and a maximum deviation of 21 cm(-1) (<2%). The only IR peak assigned to the linear uranyl moiety was the asymmetric ν3 mode, which appeared at 965 cm(-1) and was predicted by DFT as 953 cm(-1). This ν3 frequency is red-shifted relative to bare uranyl, UO2(2+), by ca. 150 cm(-1) due to electron donation from the TMOGA ligands. Based on the degree of red-shifting, it is inferred that two TMOGA oxygen-donor ligands have a greater effective gas basicity than the four monodentate acetone ligands in UO2(acetone)4(2+). The uranyl ν3 frequency was also computed for uranyl coordinated by two TMGA ligands, in which the central Oether of TMOGA has been replaced by CH2. The computed ν3 for UO2(TMGA)2(2+), 950 cm(-1), is essentially the same as that for UO2(TMOGA)2(2+), suggesting that electron donation to uranyl from the Oether of TMOGA is minor. The computed ν3 asymmetric stretching frequencies for the three actinyl complexes, UO2(TMOGA)2(2+), NpO2(TMOGA)2(2+) and PuO2(TMOGA)2(2+), are comparable. This similarity is discussed in the context of the relationship between ν3 and intrinsic actinide-oxygen bond energies in actinyl complexes.
authors.affiliation: †Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson
authors.forename: Han-Shi
authors.initials: HS
authors.lastname: Hu
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.affiliation: ∥Institute for Molecules and Materials, FELIX Laboratory, Radboud University Nijmegen, Toernooiveld 7, 6525ED Nijmegen, The Netherlands.
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.affiliation: ∥Institute for Molecules and Materials, FELIX Laboratory, Radboud University Nijmegen, Toernooiveld 7, 6525ED Nijmegen, The Netherlands.|⊥van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.affiliation: #William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
authors.forename: Jun
authors.initials: J
authors.lastname: Li