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 H-2, to form the final metal-carbene complex Ptn+/-CH2,. 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. (C) 2000 Elsevier Science B.V. All rights reserved.