Effect of charge upon metal cluster chemistry: Reactions of Nbn and Rhn anions and cations with benzene

The reactions of anionic niobium and rhodium clusters Mn−, M=Nb, Rh, n=3–28, with C6H6 are investigated under single collision conditions in a Fourier-transform ion-cyclotron-resonance mass spectrometer and compared with the results of previous studies on corresponding cationic species. This reveals strong effects of the cluster charge state on hydrocarbon activation as a function of cluster size. Both differences and parallels are observed for reactions of anions and cations. Niobium clusters with a given number of atoms react quite differently than those with a single atom more or less. The fact that almost identical such effects are in the present work found for anion clusters, as for cations with the same number of atoms but two less electrons, suggests that the observed reactivity patterns are more a function of the cluster shape and geometry, than of the details of their electronic structure. The variety of interesting trends and effects observed is interpreted in terms of simple physical models.