Structure and Stability of Palladium−Carbon Cations

Abstract

A theoretical study has been carried out to explore various isomers of palladium−carbon cations, PdC_x^+. By using the B3LYP density functional method, the geometries have been optimized for linear PdC_x+ as well as several classes of cyclic, bicyclic, and graphitic isomers. Linear clusters are shown to be the most stable isomers for x < 10, which is contrary to the previously studied behavior of lanthanum, an early transition metal. For larger systems, several classes of ring-containing structures are more stable than the linear isomers. Experimental ion mobility studies of the PdC_x^+ clustering process reveal monocyclic rings for x > 10, a result consistent with the B3LYP prediction of rings as the most stable isomer. The ion mobility experiments did not produce any results for x < 10, which may be due to the reactivity of the linear PdC_x^+, which are predicted by B3LYP to be the most stable isomers at those sizes. Bicyclic PdC_(20)^+ is shown to be less stable than the monocyclic rings, but the appearance of bicyclic PdC_(20)^+ in the ion mobility experiments is explained as the result of binary collisions since it is stable with respect to PdC_(10)^+ and C_(10) rings. Graphitic PdC_(20)^+ is shown to be more stable than either monocyclic or bicyclic rings, although the graphitic sheets do not appear in the ion mobility experiments until PdC_(26)^+.