Mixing Laser Spectroscopy and Mass Spectrometry-Infrared Spectra of Metal Cation–Hydrogen Complexes

Dryza, Viktoras; Poad, Berwyck L. J.; Bieske, Evan J.

doi:10.1255/ejms.1049

Cited by 5 publications

(9 citation statements)

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“…First-row transition metal complexes such as Mn + (CH 4 ) 1−6 [ 75 ], Fe + (CH 4 ) 1−4 [ 76 ], Co + (CH 4 ) 1−4 and Ni + (CH 4 ) 1−4 [ 77 ] have also been investigated via IR photofragmentation spectroscopy [ 75 ]. The Fe + , Co + and Ni + ions, with their 3 d n ground state configurations, interact with methane more strongly than ions with 3 d n −1 4 s 1 configurations, such as Mn + (CH 4 ) 1−6 .…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

et al. 2017

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solvation, counterion, or defect effects. In turn, these shed light on the mechanism by which ligand activation occurs, leading to enhanced understanding of catalytic reactivity. Many industrial heterogeneous catalysts typically comprise multiple components, with reactions assumed to occur at metal defects supported by a macroscopic bulk structure [1]. The model systems studied can capture some of the features and energetics of the surface of catalysts [2], without complications arising from the bulk structure. The simplified nature of these model complexes also makes them tractable to theoretical studies which, coupled with experimental data, can provide a deeper understanding of fundamental interactions involved. These studies are often too computationallyintensive to perform rigorously on real systems.The interaction and reaction of methane with transition metal ions is of particular practical interest. As the simplest saturated hydrocarbon, methane serves as a key model for understanding metal ion-hydrocarbon systems. The activation of methane is an intensively studied topic in catalysis [3][4][5]. Methane is the primary component in natural gas (typically 80-90%-[4]) and with depleting petroleum reserves, the possibility of easily converting methane to more valuable chemicals and fuels would lead to its use as an abundant hydrocarbon feedstock.For complete methane activation to occur, at least one of the four strong C-H bonds (bond dissociation energy of 439 kJ mol −1 -[6]) must undergo bond scission. This is made challenging by the paucity of low-energy empty and high-energy filled orbitals in methane, making it relatively inert to reaction under most conditions [3]. The classic industrial route used to convert methane into useful reagents involves the initial conversion of methane to syngas (CO + H 2 ) via steam reforming, followed by the conversion of this syngas into a range of hydrocarbons or alcohols [3][4][5]. Despite representing a useful H 2 source, the steam Abstract A combined spectroscopic and computational study of gas-phase Au + (CH 4 ) n (n = 3-8) complexes reveals a strongly-bound linear Au + (CH 4 ) 2 core structure to which up to four additional ligands bind in a secondary coordination shell. Infrared resonance-enhanced photodissociation spectroscopy in the region of the CH 4 a 1 and t 2 fundamental transitions reveals essentially free internal rotation of the core ligands about the H 4 C-Au + -CH 4 axis, with sharp spectral features assigned by comparison with spectral simulations based on density functional theory. In separate experiments, vibrationally-enhanced dehydrogenation is observed when the t 2 vibrational normal mode in methane is excited prior to complexation. Clear infrared-induced enhancement is observed in the mass spectrum for peaks corresponding 4u below the mass of the Au + (CH 4 ) n=2,3 complexes corresponding, presumably, to the loss of two H 2 molecules.

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Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

et al. 2017

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“…The complexes adopt an η 3 configuration, with the Fe−C bond length (2.52 Å) slightly shorter than the Mn−C bond length (2.64 Å) 19 and significantly shorter than the Al−C bond length (2.90 Å) . Accordingly, sextet Fe + (CH 4 ) (40 kJ/mol) is more strongly bound than Mn + (CH 4 ) (34 kJ/mol) and Al + (CH 4 ) (25 kJ/mol). ,, In the C−H stretching region, the vibrational spectra are also similar: each spectrum consists of a single peak due to the symmetric C−H stretch, with stronger, shorter metal−methane bonds leading to larger red shifts, from Al + (CH 4 ) (2850 cm −1 ) to Mn + (CH 4 ) (2836 cm −1 ) to sextet Fe + (CH 4 ) (2813 cm −1 ).…”

Section: Resultsmentioning

confidence: 91%

“…Comparison with calculated spectra of candidate structures show that the observed spectrum definitively establishes that the structure consists of intact CH 4 units bound to the metal in an η 3 configuration. Dryza and Bieske recently extended these studies to Mn + (CH 4 ) n ( n = 1−6) . Again, the symmetric C−H stretch dominates the spectrum.…”

Section: Introductionmentioning

confidence: 90%

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Vibrational Spectroscopy and Theory of Fe⁺(CH₄)_n (n = 1−4)

et al. 2010

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Vibrational spectra are measured for Fe(+)(CH(4))(n) (n = 1-4) in the C-H stretching region (2500-3200 cm(-1)) using photofragment spectroscopy. Spectra are obtained by monitoring CH(4) fragment loss following absorption of one photon (for n = 3, 4) or sequential absorption of multiple photons (for n = 1, 2). The spectra have a band near the position of the antisymmetric C-H stretch in isolated methane (3019 cm(-1)), along with bands extending >250 cm(-1) to the red of the symmetric C-H stretch in methane (2917 cm(-1)). The spectra are sensitive to the ligand configuration (η(2) vs η(3)) and to the Fe-C distance. Hybrid density functional theory calculations are used to identify possible structures and predict their vibrational spectra. The IR photodissociation spectrum shows that the Fe(+)(CH(4)) complex is a quartet, with an η(3) configuration. There is also a small contribution to the spectrum from the metastable sextet η(3) complex. The Fe(+)(CH(4))(2) complex is also a quartet with both CH(4) in an η(3) configuration. For the larger clusters, the configuration switches from η(3) to η(2). In Fe(+)(CH(4))(3), the methane ligands are not equivalent. Rather, there is one short and two long Fe-C bonds, and each methane is bound to the metal in an η(2) configuration. For Fe(+)(CH(4))(4), the calculations predict three low-lying structures, all with η(2) binding of methane and very similar Fe-C bond lengths. No single structure reproduces the observed spectrum. The approximately tetrahedral C(1) ((4)A) structure contributes to the spectrum; the nearly square-planar D(2d) ((4)B(2)) and the approximately tetrahedral C(2) ((4)A) structure may contribute as well.

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“…Given these structural trends, a reasonable question concerns the experimental observation of such properties. Mass spectrometry, as well as rotational and vibrational spectroscopy, of singly charged metal ions (ranging from Li + to Cr + ) bound to a dihydrogen ligands has been studied both experimentally − and computationally. ,, Backing structural information out of these highly fluxional complexes is challenging, although such theory–experiment studies hold promise. These approaches should be extendable to the divalent ions, with additional ligands, and such experimental analysis is encouraged here.…”

Section: Resultsmentioning

confidence: 99%

Nuclear Motion in the σ-Bound Regime of Metal–H₂Complexes: [Mg(H₂)_n=1–6]²⁺

Mitchell

Steele

2014

J. Phys. Chem. A

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The dynamic, quantum structure of [Mg(H2)(n=1-6)](2+)complexes is investigated via ab initio path integral molecular dynamics simulations. These complexes represent the strong, σ-complex regime of metal-H2 interactions and are representative of bonding motifs found in metal-organic frameworks. Significant nuclear motion within the coordination sphere is observed, even though the ligands remain largely intact. Quantum effects are found to be important in the H-H and metal-H2 stretch coordinates, but the remaining motion in the molecule is well represented by classical simulations. Nearly free rotation of the dihydrogen moiety is observed in all complexes. Statistical averages and distributions of structural parameters are found to deviate nontrivially from the same parameters in static, equilibrium structures.

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Mixing Laser Spectroscopy and Mass Spectrometry-Infrared Spectra of Metal Cation–Hydrogen Complexes

Cited by 5 publications

References 24 publications

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

Vibrational Spectroscopy and Theory of Fe⁺(CH₄)_n (n = 1−4)

Nuclear Motion in the σ-Bound Regime of Metal–H₂Complexes: [Mg(H₂)_n=1–6]²⁺

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Mixing Laser Spectroscopy and Mass Spectrometry-Infrared Spectra of Metal Cation–Hydrogen Complexes

Cited by 5 publications

References 24 publications

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C–H Activation Reactions

Vibrational Spectroscopy and Theory of Fe+(CH4)n (n = 1−4)

Nuclear Motion in the σ-Bound Regime of Metal–H2Complexes: [Mg(H2)n=1–6]2+

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Vibrational Spectroscopy and Theory of Fe⁺(CH₄)_n (n = 1−4)

Nuclear Motion in the σ-Bound Regime of Metal–H₂Complexes: [Mg(H₂)_n=1–6]²⁺