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Methane activation by gold-doped titanium oxide cluster anions with closed-shell electronic structures.

ABSTRACT: The reactivity of closed-shell gas phase cluster anions AuTi₃O₇^- and AuTi₃O₈^- with methane under thermal collision conditions was studied by mass spectrometric experiments and quantum chemical calculations. Methane activation was observed with the formation of AuCH₃ in both cases, while the formation of formaldehyde was also identified in the reaction system of AuTi₃O₈^-. The cooperative effect of the separated Au⁺ and O^2- ions on the clusters induces the cleavage of the first C-H bond of methane. Further activation of the second C-H bond by a peroxide ion O₂^2- leads to the formation of formaldehyde. This study shows that closed-shell species on metal oxides can be reactive enough to facilitate thermal H-CH₃ bond cleavage and the subsequent conversion.

SUBMITTER: Zhao YX

PROVIDER: S-EPMC6016522 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

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Methane activation by gold-doped titanium oxide cluster anions with closed-shell electronic structures.

Zhao Yan-Xia YX Li Xiao-Na XN Yuan Zhen Z Liu Qing-Yu QY Shi Qiang Q He Sheng-Gui SG

Chemical science 20160329 7

The reactivity of closed-shell gas phase cluster anions AuTi3O7- and AuTi3O8- with methane under thermal collision conditions was studied by mass spectrometric experiments and quantum chemical calculations. Methane activation was observed with the formation of AuCH3 in both cases, while the formation of formaldehyde was also identified in the reaction system of AuTi3O8-. The cooperative ...[more]

PMID: 30155123

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Project description:A series of oligothiophene bis(dioxolene) complexes, SQ-Thn-SQ (SQ = S = ½TpCum,MeZnII(3-tert-butyl-orthosemiquinonate); TpCum,Me = tris(5-cumenyl-3-methylpyrazolyl)borate anion) have been synthesized, structurally characterized, and studied as a function of the number of thiophene bridging units, n (n = 0-3) using a combination of variable-temperature (VT) electronic absorption and EPR spectroscopies, and VT magnetic susceptibility measurements. The thiophene bridge bond lengths determined by X-ray crystallography display dramatic differences across the SQ-Thn-SQ series. Bridge bond deviation values (Σ|Δi|) display a progressive change in the nature of the bridge fragment bonding as the number of thiophene groups increases, with quinoidal bridge character for n = 1 (SQ-Th-SQ) and biradical character with "aromatic" bridge bond lengths for n = 3 (SQ-Th3-SQ). Remarkably, for n = 2 (SQ-Th2-SQ) the nature of the bridge fragment is intermediate between quinoid and biradical aromatic, which we describe as having open-shell character as opposed to biradicaloid since the open-shell biradical configuration does not have the correct symmetry to mix with the quinoidal ground-state configuration. This bridge bonding character is reflected in the energies of the lowest lying open-shell states for these three molecules. The SQ-Th-SQ molecule is diamagnetic at all temperatures studied, and we provide evidence for SQ-SQ antiferromagnetic exchange coupling and population of triplet states in SQ-Th2-SQ and SQ-Th3-SQ, with JSQ-SQ(ave) = -279 cm-1 (VT EPR/electronic absorption/magnetic susceptibility) and JSQ-SQ = -117 cm-1 (VT EPR/electronic absorption/magnetic susceptibility), respectively. The results have been interpreted in the context of state configurational mixing within a simplified 4-electron, 3-orbital model that explicitly contains contributions of a bridge fragment. Variable-temperature spectroscopic- and magnetic susceptibility data are consistent with two low-lying open-shell states for SQ-Th3-SQ, but three low-lying states (one closed-shell and two open-shell) for SQ-Th2-SQ. This model provides a simple symmetry-based framework to understand the continuum of electronic and geometric structures of this class of molecules as a function of the number of thiophene units in the bridge.

Dataset Information

Methane activation by gold-doped titanium oxide cluster anions with closed-shell electronic structures.

Publications

Methane activation by gold-doped titanium oxide cluster anions with closed-shell electronic structures.

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