Theoretical study of hydrogenation of the doubly aromatic B7− cluster
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- Alexandrova, A.N., Koyle, E. & Boldyrev, A.I. J Mol Model (2006) 12: 569. doi:10.1007/s00894-005-0035-5
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We have studied the influence of hydrogenation on the relative stability of the low-lying isomers of the anionic B7− cluster, computationally. It is known that the pure-boron B7− cluster has a doubly (σ- and π-) aromatic C6v (3A1) quasi-planar wheel-type triplet global minimum (structure 1), a low-lying σ-aromatic and π-antiaromatic quasi-planar singlet C2v (1A1) isomer 2 (0.7 kcal mol−1 above the global minimum), and a planar doubly (σ- and π-) antiaromatic C2v (1A1) isomer 3 (7.8 kcal mol−1 above the global minimum). However, upon hydrogenation, an inversion in the stability of the species occurs. The planar B7H2− (C2v, 1A1) isomer 4, originated from the addition of two hydrogen atoms to the doubly antiaromatic B7− isomer 3, becomes the global minimum structure. The second most stable B7H2− isomer 5, originated from the quasi-planar triplet wheel isomer 1 of B7−, was found to be 27 kcal mol−1 higher in energy. The inversion in stability occurs due to the loss of the doubly aromatic character in the wheel-type global minimum isomer (C6v, 3A1) of B7− upon H2−addition. In contrast, the planar isomer of B7− (C2v, 1A1) gains aromatic character upon addition of two hydrogen atoms, which makes it more stable.