Experimental Identification of the Active Site in the Heteronuclear Redox Couples [AlVO_x]^+./CO/N₂O (x=3, 4) by Gas‐Phase IR Spectroscopy

Abstract

Cryogenic ion vibrational spectroscopy was used in combination with electronic structure calculations to identify the active site in the oxygen atom transfer reaction [AlVO ] +CO→[AlVO ] +CO . Infrared photodissociation spectra of messenger-tagged heteronuclear clusters demonstrate that in contrast to [AlVO ] , [AlVO ] is devoid of a terminal Al-O unit while the terminal V=O group remains intact. Thus it is the Al-O moiety that forms the active site in the [AlVO ] /CO/N O (x=3, 4) redox couples, which is in line with theoretical predictions.

Identification of Active Sites and Structural Characterization of Reactive Ionic Intermediates by Cryogenic Ion Trap Vibrational Spectroscopy

“…While time‐honored labeling experiments provided some mechanistic insight on the reaction, they did not help to experimentally identify the active site of the cluster oxide. This crucial issue was recently resolved by cryogenic ion trap vibrational spectroscopy, and the result is unambiguous and confirms the theoretical predictions.…”

“…The obtained time‐of‐flight mass spectrum shows that also under multiple collision conditions [AlVO 4 ] .+ is very efficiently (>98 %) converted to [AlVO 3 ] .+ . Additional reactions with CO molecules cannot be avoided under the present conditions, but exclusively lead to “solvated” [AlVO 3 ] .+ clusters of the type [AlVO 3 ] .+ ⋅(CO) x ( x =0–7), of which the [AlVO 3 ] .+ ⋅(CO) 6 complex is formed predominantly . Its IRPD spectrum, obtained by monitoring the CO loss channels, is shown in Figure (panel III).…”

“…This experiment had to be performedwith CO seededi nH eg as at slightly highert emperatures ( 6 complex is formed predominantly. [100] Its IRPD spectrum,o btained by monitoring the CO loss channels, is shown in Figure 5( panel III). The comparison with the simulated IR spectra of isomers 5·(CO) 6 and 6·(CO) 6 clearlyd emonstrates that it is indeedt he main-group aluminum oxide whichd elivers its oxygen atom in the redox process.…”

“…The simulated IR spectrawere determined from scaled B3LYP-D3(BJ)/cc-pVTZ harmonic frequencies and intensities and convoluted with a 10 cm À1 full width at half-maximumGaussian line shapef unction. Adapted from Ref [100]…”

Direct Identification of Acetaldehyde Formation and Characterization of the Active Site in the [VPO4].+/C2H4 Couple by Gas‐Phase Vibrational Spectroscopy

“…DFT calculations have provided insight into the mechanism of this OAT catalytic cycle and predicted the terminal Al−O and not the expected V−O unit as the active site of the catalyst . Experimental confirmation of these predictions for both the structure of the [AlVO 4 ] .+ cluster oxide as well as its active site was only obtained much later by cryogenic ion‐trap vibrational spectroscopy of messenger‐tagged cluster ions …”