Structure of the Oxygen-Rich Cluster Cation Al2O7+ and its Reactivity toward Methane and Water

The oxygen-rich cluster Al2O7+ is generated in the gas phase and investigated with respect to both its structure and its reactivity toward small, inert molecules using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry and DFT-based calculations. Al2O7+ reacts with CH4 under ambient conditions via hydrogen atom transfer (HAT), and with H2O a ligand exchange occurs which gives rise to the evaporation of two O-2 molecules. The resulting product ion Al2O4H2+ is also capable of abstracting a hydrogen atom from both H2O and CH4. As indicated in the H2O/2O(2) ligand exchange and supported by collision-induced dissociation (CID) experiments, two O-2 units constitute structural elements of Al2O7+. Further insight is provided by DFT calculations, performed at the unrestricted B3LYP/TZVP level, and reaction mechanisms are suggested on the basis of both the experimental and theoretical results.