Vibrational spectroscopy of free di-manganese oxide cluster complexes with di-hydrogen

Abstract

The reaction of free di-manganese oxide clusters Mn₂O_x⁺ (x = 2-7) with hydrogen in a flow tube reactor results in a strongly cluster size dependent complex formation: Mn₂O₃⁺ and Mn₂O₄⁺ are most reactive and adsorb up to two H₂ molecules, the reactivity is reduced for Mn₂O₂⁺/Mn₂O₅⁺, and Mn₂O₆⁺/Mn₂O₇⁺ appear to be non-reactive. Infrared multiple-photon dissociation (IR-MPD) spectra of the complexes Mn₂O₄H₂⁺ and Mn₂O₅H₂⁺ reveal one band that shifts upon isotopic labelling of hydrogen, whereas the spectra of Mn₂O₂H₂⁺ and Mn₂O₃H₂⁺ do not show any clear spectral shifts upon H₂/D₂ exchange. Detailed analysis of the IR-MPD spectra in conjunction with density functional theory (DFT) calculations strongly indicate the molecular η²-binding of H₂ to one of the Mn atoms. H₂ dissociation via hydroxylation of the cluster oxo bridges yielding H-Mn(MH)O(OH)O₂⁺ or Mn₂(OH)₂O₂⁺ appears to be thermodynamically favourable but kinetically hampered.

GRAPHICAL ABSTRACT

KEYWORDS:

• Manganese oxide
• hydrogen evolution reaction
• gasphase
• infrared spectroscopy
• DFT calculations

Acknowledgements

T. M. B, and S. M. L. thank the Deutsche Forschungsgemeinschaft for financial support and Dr. Nina Zimmermann for experimental assistance. We gratefully acknowledge the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) for the support of the FELIX Laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research leading to these results has received funding from LASERLAB-EUROPE (grant agreement no. 654148, European Union’s Horizon 2020 research and innovation programme). Computations were carried out at the Georgia Tech Center for Computational Materials Science. U. L. and B. Y. were supported by the Air Force Office for Scientific Research (AFOSR) grant FA9550-21-1-0198.