Haijun Jiao

On the basis of the experimental Gibbs free-energy barrier of the degenerate Cope arrangement in semibullvalene, B3P86 shows the best agreement, while B3LYP and MP2 underestimate and CCSD(T) overestimates the barrier. The substituent effect proposal by Hoffmann has been verified. In contrast to semibullvalenes with either localized energy-minimum structures or delocalized transition-state structures, perfluorosemibullvalene has both localized and delocalized energy-minimum structures that are very close in energy. Localized and delocalized perfluorosemibullvalenes

The structure and stability of neutral polyoxometalate cages (Mo₂O₆) _m (m=1–13) have been computed systematically. These neutral cages can be viewed topologically as polyhedra containing triangles (f ₃) and squares (f ₄). The relative stability of these polyhedra is associated with the location and separation of the f ₃. The initial stable isomers were preselected by the number of shared triangle edges (N ₃₃), and the predicted stability was validated further at the GGA-PW91/DND level of density function theory with the fine quality of mesh size. For large clusters, the square neighbor signature (P ₄₄₄₄), which is similar to the hexagon neighbor rule for fullerene, becomes more applicable. The calculated disproportionation energies indicate that Mo₆O₁₈ (O _h, Lindqvist), Mo₁₂O₃₆ (O _h, α Keggin), Mo₁₈O₅₄ (D _3h, Wells–Dawson) and Mo₂₄O₇₂ (O _h) cages have enhanced stability. Mo₆O₁₈ (O _h), Mo₁₂O₃₆ (O _h), Mo₁₈O₅₄ (D _3h) and Mo₂₄O₇₂ (O _h) are the most stable neutral polyoxometalate cages on the basis of the structural and energetic criteria. They can therefore be considered as the inorganic fullerenes

The structures and stabilities of square–hexagon alternant boron nitrides (B _x N _x , x=12–36) vs their tube isomers containing octagons, decagons and dodecagons have been computed at the B3LYP density functional level of theory with the correlation-consistent cc-pVDZ basis set of Dunning. It is found that octagonal B₂₀N₂₀ and B₂₄N₂₄ tube structures are more stable than their square–hexagon alternants by 18.6 and 2.4 kcal mol⁻¹, respectively, while the square–hexagon alternants of other cages are more stable. Trends in stability as a function of cluster size are discussed.