Anion Photoelectron Spectroscopy and Theoretical Studies of Al4C6-/0: Global Minimum Triangle-Shaped Structures and Hexacoordinated Aluminum.

Anion photoelectron spectroscopy and theoretical calculations were used to investigate the structural and bonding properties of Al4C6-/0 clusters. The vertical detachment energy of Al4C6- was measured to be 3.36 ± 0.08 eV. The structure of the Al4C6- anion is confirmed to be a bowl-shaped distorted triangle with an Al atom at the center and three Al atoms at the vertices. The global minimum isomer of neutral Al4C6 has a planar triangle-shaped structure with D3h symmetry. Both anionic and neutral Al4C6 have a hexacoordinated Al atom surrounded by three C≡C groups. Compared with the structure of neutral Al4C6, the structure of Al4C6- is distorted due to the addition of the excess electron. The molecular orbital analysis shows that the singly occupied molecular orbital of Al4C6- mainly locates on one side of the triangle plane and the neutral Al4C6 has a large highest occupied molecular orbital and lowest unoccupied molecular orbital gap. Theoretical calculations indicate that neutral Al4C6 has some aromaticity.