Methane activation by platinum cluster ions in the gas phase: Effects of cluster charge on the Pt₄ tetramer

The reactions of cationic and anionic platinum clusters Pt^±_n, n=1-9, with methane CH₄ are investigated under single collision conditions in a Fourier-Transform Ion Cyclotron Resonance Mass Spectrometer. The reaction of the platinum clusters proceeds through the activation of C-H bonds of methane and leads to the subsequent elimination of molecular hydrogen H₂ to form the final metal-carbene complex Pt^±_nCH₂. The cation cluster reactions proceed in general with collision rate whereas the anion cluster reactions are more than an order of magnitude slower. The platinum tetramer anion is unique among all the clusters studied, reacting more efficiently than the corresponding cation. Tentative interpretation in terms of electronic and geometric effects is performed.