Infrared photodissociation spectroscopy of di-manganese oxide cluster cations

Abstract

Infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional theory (DFT) calculations have been employed to elucidate the geometric structure of a series of di-manganese oxide clusters Mn₂O_x⁺ (x = 4–7). The theoretical exploration predicts that all investigated clusters contain a rhombus-like Mn₂O₂ core with up to four, terminally bound, oxygen atoms. The short Mn–O bond length of the terminal oxygen atoms of ≤1.58 Å indicates triple bond character instead of oxyl radical formation. However, the IR-MPD spectra reveal that higher energy isomers with up to two O₂ molecules η²-coordinated to the cluster core can be kinetically trapped under the given experimental conditions. In these complexes, all O₂ units are activated to superoxide species. In addition, the sequential increase of the oxygen content in the cluster allows for a controlled increase of the positive charge localized on the Mn atoms reaching a maximum for Mn₂O₇⁺.