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

Based upon global-minimum searches and first-principles electronic structural calculations, we present the perfectly planar B6O50/-/2- (1-3) systems. Notably, the C2v B6O50/- (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 Cs 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)n0/- (n = 1-5) series and provides valuable perspectives on their structural evolution.