Abstract
The reaction of free di-manganese oxide clusters Mn2Ox+ (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.
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).