B7- as a novel ligand: Theoretical investigations on structures and chemical bonding of LiB7 and BeB7+

The double HOMO and single HOMO−4 are π-bonding orbitals, occupied by four electrons, rendering π-aromaticity. The double HOMO−1 and single HOMO−3 are σ orbitals, occupied by six electrons, rendering σ-aromaticity. Thus, triplet (C6v, 3A1) LiB7 species posses doubly (σ- and π-) aromaticity.