Structures of Mo2Oy− and Mo2Oy (y=2, 3, and 4) studied by anion photoelectron spectroscopy and density functional theory calculations

Abstract

The competitive structural isomers of the Mo(2)O(y) (-)Mo(2)O(y) (y=2, 3, and 4) clusters are investigated using a combination of anion photoelectron (PE) spectroscopy and density functional theory calculations. The PE spectrum and calculations for MoO(3) (-)MoO(3) are also presented to show the level of agreement to be expected between the spectra and calculations. For MoO(3) (-) and MoO(3), the calculations predict symmetric C(3v) structures, an adiabatic electron affinity of 3.34 eV, which is above the observed value 3.17(2) eV. However, there is good agreement between observed and calculated vibrational frequencies and band profiles. The PE spectra of Mo(2)O(2) (-) and Mo(2)O(3) (-) are broad and congested, with partially resolved vibrational structure on the lowest energy bands observed in the spectra. The electron affinities (EA(a)s) of the corresponding clusters are 2.24(2) and 2.33(7) eV, respectively. Based on the calculations, the most stable structure of Mo(2)O(2) (-) is Y shaped, with the two Mo atoms directly bonded. Assignment of the Mo(2)O(3) (-) spectrum is less definitive, but a O-Mo-O-Mo-O structure is more consistent with overall electronic structure observed in the spectrum. The PE spectrum of Mo(2)O(4) (-) shows cleanly resolved vibrational structure and electronic bands, and the EA of the corresponding Mo(2)O(4) is determined to be 2.13(4) eV. The structure most consistent with the observed spectrum has two oxygen bridge bonds between the Mo atoms.

H 2 production from reactions between water and small molybdenum suboxide cluster anions

“…The factor of 3 difference in k 4b between the molybdenum and tungsten analogs may indeed be related to structure. The lowest energy isomer determined for W 2 O 5 − has a symmetric structure in which the two W-centers have two terminal O-atoms, and are bound to each other by a single oxygen bridge bond, 38,39 while calculations on Mo 2 O 5 − predict that this structure is nearly isoenergetic with a structure featuring two bridge bonds and one metal center with only one terminal O-atom ͑with two competitive open-shell electronic states͒. 39 The plausibility of a structure in which one metal center is more reduced ͑and unhindered͒ relative to the other suggests that this may be the source of the higher k 4b rate constant for Mo 2 41 it was determined that the lowest energy isomers of both Mo 3 O 6 − and W 3 O 6 − are C 3v structures with 2 A 1 electronic states, and similar adiabatic and vertical detachment energies.…”

Observation of d‐Orbital Aromaticity

“…[24][25][26] We investigated the structure and bonding of early transition metal oxide clusters using a combined photoelectron spectroscopy (PES) and theoretical approach with the aim of discovering specific structures or clusters that may mimic a catalytic site. [27,28] Our experiment was carried out with a magnetic-bottle PES apparatus with a laser vaporization cluster source.…”

Structures of MoxW(3−x)O6 (x=–3) anion and neutral clusters determined by anion photoelectron spectroscopy and density functional theory calculations

“…All four species show broad electronic transitions above an electron binding energy of 2.5 eV which is comparable to the EA ad 's of Mo 2 O 4 , W 2 O 4 , and MoWO 4 determined in previous studies. 13,20,24 The PE spectrum of Mo 3 O 6 − , shown in the top panel of Fig. 1, exhibits a sharp onset of signal at eBE= 2.73͑2͒ eV, with a partially resolved, ϳ300 cm −1 vibrational progression.…”

“…19 Anion PE spectroscopy is a technique that is well suited to the study of these very complicated transition metal oxide clusters, particularly when coupled with calculations. [20][21][22][23][24] The anion PE spectra of Mo 3 O 6 − and W 3 O 6 − along with calculations on the anion and neutral species predict that these clusters have nearly identical low-spin cyclic structures, with loss of symmetry calculated for the lowest energy structures of the binary anions. However, the cyclic species are predicted to have stable low-spin states, in sharp contrast to the Mo 2 O 4 , W 2 O 4 , and MoWO 4 anion and neutral clusters having the same metal-oxygen ratio.…”

“…The anion PE spectrometer used in this study has been described in detail elsewhere, 20 and only a brief description follows. A distribution of pure and binary metal oxide cluster anions is generated in a laser ablation/pulsed molecular beam source similar to that developed by Dietz et al 25 Approximately 10 mJ/pulse of the 532 nm second harmonic output of a Nd:YAG ͑yttrium aluminum garnet͒ laser operated at a 30 Hz repetition rate is focused onto a pressed powder mixture composed of approximately 40% mole fraction of 186 W and 98 Mo ͑Oak Ridge National Laboratory, Isotope Business Of-fice͒.…”