Planar dicyclic B₆S₆, B₆S₆⁻, and B₆S₆²⁻ clusters: Boron sulfide analogues of naphthalene

Inorganic analogues of hydrocarbons or polycyclic aromatic hydrocarbons (PAHs) are of current interest in chemistry. Based upon global structural searches and B3LYP and CCSD(T) calculations, we present herein the perfectly planar dicyclic boron sulfide clusters: D_2h B₆S₆ (1, ¹A_g), D_2h B₆S₆⁻ (2, ²B_3u), and D_2h B₆S₆²⁻ (3, ¹A_g). These are the global minima of the systems, being at least 0.73, 0.81, and 0.53 eV lower in energy, respectively, than their alternative isomers at the CCSD(T) level. The D_2h structures feature twin B₃S₂ five-membered rings, which are fused together via a B₂ unit and terminated by two BS groups. Bonding analyses show that the closed-shell B₆S₆²⁻ (3) cluster possesses 10 delocalized π electrons, closely analogous to the bonding pattern of the aromatic naphthalene C₁₀H₈. The B₆S₆⁻ (2) and B₆S₆ (1) species are readily obtained upon removal of one or two π electrons from B₆S₆²⁻ (3). The results build a new analogous relationship between boron sulfide clusters and their PAH counterparts. The B₆S₆⁻ (2) monoanion and B₆S₆²⁻ (3) dianion can be effectively stabilized in neutral LiB₆S₆ and Li₂B₆S₆ salts, respectively