Boron Oxide B(5)O(6) (−) Cluster as a Boronyl-Based Inorganic Analog of Phenolate Anion

Boron oxide clusters have structural richness and exotic chemical bonding. We report a quantum chemical study on the binary B(5)O(6) (−) cluster, which is relatively oxygen-rich. A global structural search reveals planar C (2v ) ((1)A(1)) geometry as the global minimum structure, featuring a heteroatomic hexagonal B(3)O(3) ring as its core. The three unsaturated B sites are terminated by two boronyl (BO) groups and an O(−) ligand. The B(5)O(6) (−) cluster can be faithfully formulated as B(3)O(3)(BO)(2)O(−). This structure is in stark contrast to that of its predecessors, C ( s ) B(5)O(5) (−) and T ( d ) B(5)O(4) (−), both of which have a tetrahedral B center. Thus, there exists a major structural transformation in B(5)O( n ) (−) series upon oxidation, indicating intriguing competition between tetrahedral and heterocyclic structures. The chemical bonding analyses show weak 6π aromaticity in the B(5)O(6) (−) cluster, rendering it a boronyl analog of phenolate anion (C(6)H(5)O(−)) or boronyl boroxine. The calculated vertical detachment energy of B(5)O(6) (−) cluster is 5.26 eV at PBE0, which greatly surpasses the electron affinities of halogens (Cl: 3.61 eV), suggesting that the cluster belongs to superhalogen anions.