Abstract
We investigate the structure of copper formate and deuterated copper formate clusters using infrared multiple photon dissociation in combination with quantum chemical calculations. Symmetric and asymmetric C-O stretching vibrations along with C-H/C-D stretching vibrations were characterized. Fermi interactions between the C-H stretch and likely a C-O combination band and/or the overtone of a C-H in-plane bending motion have been confirmed by deuteration. The spectra reveal a strong dependence on the monodentate or bidentate binding motif of the formate ligands. Many minima are energetically accessible on the potential energy surface through rotation of the monodentate formate ligands into several almost isoenergetic local minima. While the C-H/C-D stretching vibration is heavily influenced by the charge distribution in the cluster, the C-O vibrations are largely unaffected. The C-H stretch region is not very diagnostic due to a variety of possible Fermi resonances, which also depend on the charge distribution at the formate ligand. Deuteration yields unperturbed spectra in the C-D stretch region and reveals characteristic shifts of the C-D stretching mode for the different binding motifs, with a strong dependence of the band position on the oxidation state of the copper center. The observed bands are compared with formate adsorbed on copper surfaces from the literature.
Highlights
The mechanisms behind the efficient activation of the rather inert CO2 molecule have become an increasingly large research field.[1]
Based on quantum chemical calculations, the first band at 1303 cm−1 is assigned to the mixed symmetric C–O vibration on the monodentate formate ligands with the C–H in-plane bending motion on the bidentate ligand at 1292 cm−1
We investigated the structure and vibrations of copper formate clusters using Infrared Multiple Photon Dissociation (IRMPD) in combination with quantum chemical calculations
Summary
The mechanisms behind the efficient activation of the rather inert CO2 molecule have become an increasingly large research field.[1]. This is in line with the assignment of the spectrum of the argon-tagged isolated formate anion,[86] which is reported to exhibit Fermi resonances from the interaction of the in-plane C–H bending overtone at about 2675 cm−1 with the fundamental C–H vibration at 2449 cm−1, similar to earlier studies in solution.[91,98,99] With the addition of the copper center, the fundamental C–H vibration is shifted significantly closer to the C–O combination bands.
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