Electronic Origin of the Competitive Mechanisms in the Thermal Activation of Methane by the Heteronuclear Cluster Oxide [Al2 ZnO4 ].

The thermal gas-phase reactions of [Al2 ZnO4 ].+ with methane have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Two competitive mechanisms, that is, hydrogen-atom transfer (HAT) and proton-coupled electron transfer (PCET) are operative. Interestingly, while the HAT process is influenced by the polarity of the transition structure, both the ionic nature of the metal-oxygen bond and the structural rigidity of the cluster oxide affect the PCET pathway. As compared to the previously reported homonuclear [Al2 O3 ].+ and [ZnO].+ , the heteronuclear oxide [Al2 ZnO4 ].+ exhibits a much higher chemoselectivity towards methane. The electronic origins of the doping effect have been explored.