Structures and chemical bonding of B6O50/−/2−: The first boron oxide clusters with five-membered ring and their structural diversity.

Based upon global-minimum searches and first-principles electronic structural calculations, we present the perfectly planar B₆O₅^0/−/2− (1–3) systems. Notably, the C_2v B₆O₅^0/− (1–2) clusters mark a groundbreaking advancement as the first boron oxide clusters to feature a five-membered ring. Both structures exhibit remarkable similarity, each characterized by a central B₃O₂ ring surrounded by three terminal BO groups. However, a notable difference lies in the bond lengths within the B₃O₂ core, which are uniform in the former but uneven in the latter. Detailed canonical molecular orbital and AdNDP analyses reveal the delocalized π bonds over the B₃O₂ ring, affirming the π aromaticity of B₆O₅⁻. The C_s B₆O₅²⁻ (3) cluster showcases a chain-like arrangement with three terminal BO groups and a typical OBO group linked to a B₂ core, emphasizing the crucial role of electrons in shaping the structure. Detailed chemical bonding analyses reveal the presence of dual three-center four-electron (3c–4e) π hyperbonds in 3, shedding further light on its unique bonding characteristics. Moreover, this study comprehensively extends the B(BO)_n^0/− (n = 1–5) series and provides valuable perspectives on their structural evolution. [ABSTRACT FROM AUTHOR]