Heterocyclic Hexagonal B5O7− and B5O8− Clusters: Inorganic Benzenes and Phenolate Anions, Dual 3C-4E Hypervalent Π Bonds, and Superhalogen Anions

Boron oxide clusters show structural diversity, unique electronic properties, and exotic chemical bonding, owing to boron's intrinsic electron deficiency. We report on the structural, electronic, and bonding properties of two boron oxide clusters, B(5)O(7)(- )and B5O8-, using computer global-minimum (GM) searches and quantum chemical calculations. These clusters have a heteroatomic B3O3 hexagonal ring as their structural core, which is terminated and chemically saturated by the boronyl, OBO, and O- ligands. Chemical bonding analyses reveal a pi sextet in the clusters, thus rendering them new members of the "inorganic benzene" family, or more precisely, inorganic analogs of phenolate anion. The latter chemical identity gives rise to their extremely high electron binding energies beyond 5.3 eV, which are electronically robust and can be classified as superhalogen anions. The terminal OBO ligands also have dual three-center four-electron (3c-4e) hypervalent pi bonds, which are a crucial mechanism that helps stabilize these boron oxide species.