In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO₃⁺ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass-selected to react with CH₄ in an ion-trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an AuO bond into an AuNb bond during the reaction.

The activation of CH bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O^−.) is an important species in CH activation. The mechanistic details of CH activation by O^−. radicals can be well understood by studying the reactions between O^−. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc₂O₃)_NO⁻ (N=1–18) clusters was observed. The reactivity of (Sc₂O₃)_NO⁻ (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc₈O₁₃⁻) and 12 (Sc₂₄O₃₇⁻). Larger (Sc₂O₃)_NO⁻ clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc₂O₃)_NO⁻ (N=1–5) clusters, which were found to contain the O^−. radicals as the active sites. The local charge environment around the O^−. radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O^−. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the CH bond activation.

Oxygen-rich scandium cluster anions ScO_3–5⁻ are prepared by laser ablation and allowed to react with n-butane in a fast-flow reactor. A time-of-flight mass spectrometer is used to detect the cluster distribution before and after the reactions. The ScO₃⁻ and ScO₄⁻ clusters can react with n-butane to produce ScO₃H⁻, ScO₃H₂⁻, and ScO₄H⁻, while the more oxygen-rich cluster ScO₅⁻ is inert. The experiment suggests that unreactive cluster isomers of ScO₃⁻ and ScO₄⁻ are also present in the cluster source. Density functional theory and ab initio methods are used to calculate the structures and reaction mechanisms of the clusters. The theoretical results indicate that the unreactive and reactive cluster isomers of ScO_3,4⁻ contain peroxides (O₂²⁻) and oxygen-centered radicals (O^.−), respectively. The mechanisms and energetics for conversion of unreactive O₂²⁻ to reactive O^.− species are also theoretically studied.