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

Abstract

The gas‐phase reaction of the heteronuclear oxide cluster [VPO4].+ with C2H4 is studied under multiple collision conditions at 150 K using cryogenic ion‐trap vibrational spectroscopy combined with electronic structure calculations. The exclusive formation of acetaldehyde is directly identified spectroscopically and discussed in the context of the underlying reaction mechanism. In line with computational predictions it is the terminal P=O and not the V=O unit that provides the oxygen atom in the barrier‐free thermal C2H4→CH3CHO conversion. Interestingly, in the course of the reaction, the emerging CH3CHO product undergoes a rather complex intramolecular migration, coordinating eventually to the vanadium center prior to its liberation. Moreover, the spectroscopic structural characterization of neutral C2H4O deserves special mentioning as in most, if not all, ion/molecule reactions, the neutral product is usually only indirectly identified.

Platonic and Archimedean solids in discrete metal-containing clusters

“…These structures have been extensively studied by M. M. Kappesm, 572 L.-S. Wang, 568,573,574 and others. 19,[575][576][577] Comparing the structure of the ligand-free systems with that of the corresponding ligand-protected atomically precise metal clusters will help ). 565 shed light on the influence of ligands on the formation of cluster structures.…”

Gas‐Phase Mechanism of O.−/Ni2+‐Mediated Methane Conversion to Formaldehyde

“…Consequently, the relevant structures are not experimentally verified, which is problematic, since DFT alone is not predictive, in particular when partially filled d‐shells of transition metal ions are involved [6n] . Therefore, in addition to the mass spectrometric investigation of the NiAl 2 O 4 + +CH 4 reaction, we use cryogenic ion trap vibrational spectroscopy [9] to determine both the reactant and product ion structures predicted by DFT. Based on these experimentally confirmed structures we propose a reaction mechanism that involves a terminal oxygen‐centered radical anion separated from a redox active Ni 2+ center and that rationalizes why NiAl 2 O 4 + activates methane yielding both formaldehyde and a methyl radical.…”

“…Moreover, neither the H 2 nor the CO adduct of 2 P2 , which correspond to NiAl 2 O 3 H 4 + and NiAl 2 O 4 CH 2 + , respectively, were detected mass spectrometrically. However, this is also not conclusive, since mass spectrometric methods typically only detect the product ions and not the neutral product(s), although there are fortitudinous exceptions in which the neutral product molecule remains bound to the product ion [9] …”

“…However, this is also not conclusive, since mass spectrometric methods typically only detect the product ions and not the neutral product(s), although there are fortitudinous exceptions in which the neutral product molecule remains bound to the product ion. [9] Although the formation of P1 is less exothermic than that of P2, it is entropically preferred due to release of the * CH 3 moiety. At 298 K and an assumed pressure of 1 atm the Gibbs free energy for P1, À 107 kJ mol À 1 , is lower than that of the highest barrier ( 2 1/ 2 2) in the pathway for the P2 generation, À 82 kJ mol À 1 , see Supporting Information Section 4.4 Table S3.…”

Similarity scores of vibrational spectra reveal the atomistic structure of pentapeptides in multiple basins

“…Advanced technologies in the gas-phase vibrational spectroscopy have made it feasible to elucidate the structure and interaction of complex molecules and clusters. Various systems have been studied to date; for example, ionic liquid, [1][2][3][4] protonated water clusters, [5][6][7][8][9][10] metal oxide clusters, [11][12][13][14][15] and so on. Conformer-selective vibrational spectra of polypeptides [16][17][18][19][20][21][22][23][24][25][26] have been measured with the usage of infrared (IR) and ultraviolet (UV) double resonance spectroscopy and supersonic jet expansions.…”