Revisiting the Bonding Nature of Pyramidane: Analogue of the CO Molecule

Abstract

Pyramidane (C(C4H4)) and its derivatives have garnered considerable interest in organic and synthetic chemistry due to their distinctive pyramidal geometry. Nevertheless, the non-classical bonding pattern between the pyramidal apex and base remains insufficiently elucidated. This work firstly developed two-dimensional (2D) superatom–atom super bonding framework, providing new insights into the bonding nature of C(C4H4). Specifically, the π-conjugated C4H4 unit acts as a 2D ◊O superatom with four π-electrons, enabling interaction with the apical carbon atom to form a CO-type superatomic molecule via a super triple bond, satisfying the electron closed shell for both the ◊O and C. Subsequently, a series of coordination complexes, Pd[C(C4H4)]n (n = 1-4), are designed to further explore the chemical bonding abilities, wherein each C(C4H4) interacts with the Pd center via a σ bond and several multicenter d-π* bonds. Moreover, we predict two stable 2D all-carbon monolayers derived from pyramidane-based assemblies, which exhibit good stability, feasible synthetic accessibility, and moderate band gaps under certain strain conditions, suggesting potential electronic applications. This work revisits the bonding paradigm of C(C4H4) and broadens our understanding of chemical interactions, offering a new strategy for the design of clusters and materials via 2D superatom–atom bonding.