An official website of the United States government
The vibrational structure and binding motifs of vanadium cation-ethane clusters, V(+)(C2H6)n, for n = 1 – 4 are probed using infrared photodissociation spectroscopy in the C-H stretching region (2550 – 3100 cm-1). Comparison of spectra to scaled harmonic frequency spectra obtained using density functional theory suggest that ethane exhibits two primary binding motifs when interacting with the vanadium cation, an end-on 𝜂2 configuration and a side-on configuration. The lower-energy side-on configuration predominates in smaller clusters, but the end-on configuration becomes important for larger clusters as it helps to maintain a roughly square planar geometry about the central vanadium. Proximate C-H bonds exhibit elongation and large red-shifts when compared to bare ethane, particularly in the case of the side-on isomer, which are underestimated by scaled harmonic frequency calculations, demonstrating initial effects of C-H bond activation.
more »
« less
This content will become publicly available on April 21, 2026
Structure and vibrational spectroscopy of complexes of Al+ and Al2+ with ethane
The binding motifs of clusters of Al+ and Al2+ with ethane, Alx+(C2H6)n (x = 1, 2; n = 1–3), are determined using vibrational photodissociation spectroscopy in the C–H stretching region (2550–3100 cm−1) in conjunction with spectra calculated using density functional theory. The relative energies of candidate structures are determined with the B3LYP-D3 and ωB97X-D density functionals and the 6–311++G(d,p) basis set. Local mode Hamiltonian calculations are better able to reproduce the spectra than scaled harmonic calculations, due to contributions from bending overtones and combination bands. Vibrational photodissociation spectra show a red shift in the stretching frequencies of C–H bonds that are proximate to the cation. This red shift decreases as the number of ethanes increases. For Al+(C2H6)n (n = 1–3), side-on (T-shaped) binding of the metal is preferred to end-on binding, and subsequent ligands bind on the same side of the cation. Similarly, for Al2+(C2H6)n (n = 1–3), T-shaped configurations in which the C–C and Al–Al bonds are approximately perpendicular and the ethane binds side-on to the Al2+ are preferred. In Al2+(C2H6)n (n = 1–3) complexes, intense bands are observed, which are due to overtones and combinations of symmetric deformations in Fermi resonance with the red-shifted C–H stretches.
more »
« less
- Award ID(s):
- 2154391
- PAR ID:
- 10618308
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 162
- Issue:
- 15
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The interaction between aluminum cations and acetone is studied in the gas phase via photodissociation vibrational spectroscopy from 1100 to 2000 cm-1. Spectra of Al+(acetone)(N2) and ions with the stoichiometry of Al+(acetone)n (n=2-5) were measured. The experimental results are compared to DFT calculated vibrational spectra to determine the structures of the complexes. The spectra show a red shift of the C=O stretch and a blue shift of the CCC stretch which decrease as the size of the clusters increases. The calculations predict that the most stable isomer for n≥3 is a pinacolate in which oxidation of the Al+ enables reductive C-C coupling between two acetone ligands. Experimentally, pinacolate formation is observed for n=5, as evidenced by a new peak observed at 1185 cm-1 characteristic of the pinacolate C-O stretch.more » « less
-
Abstract The pathways for the reactions of aluminum oxide cluster ions with ethane have been measured. For selected ions (Al2O+, Al3O2+, Al3O4+, Al4O7+) the structure of the collisionally‐stabilized reaction intermediates were explored by measuring the photodissociation vibrational spectra from 2600 cm−1–3100 cm−1. Density functional theory was used to calculate features of the potential energy surfaces for the reactions and the vibrational spectra of intermediates. Generally, more than one isomer contributes to the observed spectrum. The oxygen‐deficient clusters Al2O+and Al3O2+have large C−H activation barriers, so only the entrance channel complexes in which intact C2H6binds to aluminum are observed. This interaction leads to a substantial (~200 cm−1) red shift of the C−H symmetric stretch in ethane, indicating significant weakening of the proximal C−H bonds. In Al3O4+, the complex formed by interactions with three C2H6is investigated and, in addition to entrance channel complexes, the C−H activation intermediate Al3O4H+(C2H5)(C2H6)2is observed. For oxygen‐rich Al4O7+, the C2H6is favored to bind at an aluminum site far from the reactive superoxide group, reducing the reactivity. As expected, oxygen‐rich species and open‐shell cluster ions have smaller barriers for C−H bond activation, except for Al3O4+which is predicted and observed to be reactive.more » « less
-
Photofragment spectroscopy is used to measure the vibrational spectra of V2(+)(CH4)n (n = 1–4), V3(+)(CH4)n (n = 1–3), and Vx(+)(CH4) (x = 4–8) in the C–H stretching region (2550–3100 cm−1). Spectra are measured by monitoring loss of CH4. The experimental spectra are compared to simulations at the B3LYP+D3/6-311++G(3df,3pd) level of theory to identify the geometry of the ions. Multi-reference configuration interaction with Davidson correction (MRCI+Q) calculations are also carried out on V2(+) and V3(+). The methane binding orientation in V2(+)(CH4)n (n = 1–4) evolves from η3 to η2 as more methane molecules are added. The IR spectra of metal-methane clusters can give information on the structure of metal clusters that may otherwise be hard to obtain from isolated clusters. For example, the V3(+)(CH4)n (n = 1–3) experimental spectra show an additional peak as the second and third methane molecules are added to V3(+), which indicates that the metal atoms are not equivalent. The Vx(+)(CH4) show a larger red shift in the symmetric C–H stretch for larger clusters with x = 5–8 than for the small clusters with x = 2, 3, indicating increased covalency in the interaction of larger vanadium clusters with methane.more » « less
-
We report how the binary HNO 3 (H 2 O) interaction is modified upon complexation with a nearby Cs + ion. Isomer-selective IR photodissociation spectra of the D 2 -tagged, ternary Cs + (HNO 3 )H 2 O cation confirms that two structural isomers are generated in the cryogenic ion source. In one of these, both HNO 3 and H 2 O are directly coordinated to the ion, while in the other, the water molecule is attached to the OH group of the acid, which in turn binds to Cs + with its –NO 2 group. The acidic OH stretching fundamental in the latter isomer displays a ∼300 cm −1 red-shift relative to that in the neutral H-bonded van der Waals complex, HNO 3 (H 2 O). This behavior is analyzed with the aid of electronic structure calculations and discussed in the context of the increased effective acidity of HNO 3 in the presence of the cation.more » « less
