A density functional theory study on the electronic and adsorption characteristics of cyclo M9N9 (M = B and Al)

Exploring the Aromaticity Differences of Isoelectronic Species of Cyclo[18]carbon (C18), B6C6N6, and B9N9: The Role of Carbon Atoms as Connecting Bridges

The cyclo[18]carbon (C18) has piqued widespread interest in recent years for its geometrical aesthetic and unique electronic structure. Inspired by it, theoretical investigations of its isoelectronic B9N9 have been published occasionally; however, few studies considered their other companion B6C6N6. In this work, we study the geometric structure, charge distribution, bonding characteristic, aromaticity, and electron delocalization of B6C6N6 and B9N9 for the first time and compare the relevant results with those of C18. Based on the comprehensive analysis of aromaticity indicators such as AV1245, nucleus-independent chemical shifts, anisotropy of the induced current density, magnetically induced current density, iso-chemical shielding surface, and induced magnetic field (Bind), we found that B6C6N6 has definitely a double aromatic character similar to C18 and the aromaticities of the two are very close, while B9N9 is a nonaromatic species. In response to this novel finding, we delved into its nature from an electron delocalization perspective through a localized orbital locator, electron localization function, Fermi hole, and atomic remote delocalization index analyses. The C atom between B and N as an interconnecting bridge strengthens the electron delocalization of the conjugate path, which is the essence of the significant enhancement of the molecular aromaticity from B9N9 to B6C6N6. This work elucidates that within the framework of the isoelectronicity of C18, different methods of atomic doping can achieve molecules with completely different properties.

Model of B9N9 Response under External Electric Field: Geometry, Electronic Properties, Reaction Activity

In this paper, we performed the ωB97XD/def2-TZVP method with a density functional theory study on the boron–nitrogen (BN) analogues of cyclo[18]carbon. The geometric structure, polarization properties, and excitation effect were calculated in the presence of an external electric field (EEF). Furthermore, the dual descriptor and Fukui function matrices were employed to predict the tendency towards the electrophilic or nucleophilic reactions of B₉N₉ under varying EEF strengths. The results show that the application of an EEF will cause the cyclic structure of B₉N₉ to be considerably distorted towards an elliptical geometry, the polarization to increase, and the reactivity of B₉N₉ to enhance with the increase in the EEF strength. This is of great significance for further experimental exploration into the catalytic properties of BN fullerenes.