Structure and Stability of Palladium−Carbon Cations

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, 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)^+

Carbon Substitution on N24 Cages: Crossover between Triangular and Hexagonal Structures

Complex forms of nitrogen are of interest for their potential as high-energy materials, but many all-nitrogen systems lack the stability for practical high-energy applications. Inclusion of carbon atoms in an otherwise all-nitrogen structure can increase stability. Nitrogen cages are known for energetically preferring cylindrical structures with triangular endcaps, but carbon cages prefer the pentagon-hexagon structure of the fullerenes. Previous calculations on N22C2 have shown that carbon inclusion narrows the gap between triangular and fullerene-like structures. In the current study, three isomers of N24 are used as frameworks for carbon substitution. Theoretical calculations are carried out on isomers of N20C4, N18C6, and N16C8, with the goal of determining what level of carbon substitution causes the carbon fullerene-like structures to become energetically preferred