Infrared Multiphoton Dissociation Spectroscopy ofa Gas-Phase Complex of Uranyl and 3-Oxa-Glutaramide: An ExtremeRed-Shift of the [OUO]2+Asymmetric Stretch.

Thegas-phase complex UO2(TMOGA)22+(TMOGA= tetramethyl-3-oxa-glutaramide) prepared by electrosprayionization was characterized by infrared multiphoton dissociation(IRMPD) spectroscopy. The IRMPD spectrum from 700–1800 cm–1was interpreted using a computational study basedon density functional theory. The predicted vibrational frequenciesare in good agreement with the measured values, with an average deviationof only 8 cm–1(<1%) and a maximum deviationof 21 cm–1(<2%). The only IR peak assigned tothe linear uranyl moiety was the asymmetric ν3mode,which appeared at 965 cm–1and was predicted byDFT as 953 cm–1. This ν3frequencyis red-shifted relative to bare uranyl, UO22+, by ca. 150 cm–1due to electron donation fromthe TMOGA ligands. Based on the degree of red-shifting, it is inferredthat two TMOGA oxygen-donor ligands have a greater effective gas basicitythan the four monodentate acetone ligands in UO2(acetone)42+. The uranyl ν3frequency wasalso computed for uranyl coordinated by two TMGA ligands, in whichthe central Oetherof TMOGA has been replaced by CH2. The computed ν3for UO2(TMGA)22+, 950 cm–1, is essentiallythe same as that for UO2(TMOGA)22+, suggesting that electron donation to uranyl from the Oetherof TMOGA is minor. The computed ν3asymmetric stretchingfrequencies for the three actinyl complexes, UO2(TMOGA)22+, NpO2(TMOGA)22+and PuO2(TMOGA)22+, are comparable.This similarity is discussed in the context of the relationship betweenν3and intrinsic actinide-oxygen bond energies inactinyl complexes. [ABSTRACT FROM AUTHOR]