Unraveling the flexible aromaticity of C13H9+/0/-: a 2D superatomic-molecule theory.

Abstract

Phenalenyl (C13H9) is the smallest triangular unit of a graphene nanosheet, and has been experimentally verified to be stable in radical (C13H9˙), cationic (C13H9+), and anionic (C13H9-) states. All these three species feature high symmetry and stability as well as delocalized π electrons, a visible sign of aromaticity, but their aromatic origin remains a challenge. This work reports new chemical insights into the π electrons of C13H9+/0/- and deciphers their aromaticity using a recently emerged two-dimensional (2D) superatomic-molecule theory. 12π-C13H9+, 13π-C13H9˙, and 14π-C13H9- are seen as triangular 2D superatomic molecules ◊O3, ◊O3-, and ◊O32-, respectively, where ◊O denotes a 2D benzenoid superatom bearing 4 π electrons. Visualized superatomic Lewis structures show that each ◊O can dynamically adjust its π electrons to satisfy the superatomic sextet rule of benzene via superatomic lone pairs and covalent bonds. C13H9+/0/- are representatives of adaptive aromaticity in the 2D superatomic-molecule system, exhibiting flexible π electronic structures to achieve shell-closure. Moreover, we specially adopt a progressive methodology to study the evolution of 2D periodic materials, by applying this theory to the similar family of C6H3N7, C18H6N22 and graphitic carbon nitride (g-C3N4) crystals, and meanwhile accounting for the special stability of g-C3N4. This work enriches 2D superatomic bonding chemistry and provides a useful strategy to design new 2D functional nanostructured materials.