Properties of metal oxide clusters in non-traditional oxidation states

► Reactivity of Group 6 (Mo/W) small metal sub-oxide clusters with H2O/D2O and CO2. ► Molecular and electronic structures from PE spectra reconciled with DFT calculations. ► Asymmetric structures are particularly stable in heteronuclear clusters. ► Charge state strongly influences most stable structure of sub-oxide clusters. ► Chemical properties are influenced by asymmetric structures of heteronuclear species.