Fullerenes, carbon nanotubes and graphene as tetrel bond donors and acceptors of electrophiles

Abstract

The signs of the extrema of the molecular electrostatic surface potential (MESP) are an effective means of probing the surface reactivity behavior of molecules. They determine the electrophilicity and nucleophilicity regions, which collectively explain why one polar region of the surface of a given molecule attracts another region of opposite polarity in the same or in a neighboring molecule, resulting in the formation of molecular complexes or supramolecular assemblies in large-scale chemical systems. The chemical systems discussed in this paper are derivatives of fullerenes, carbon nanotubes and a few allotropes of graphene, that have been extensively explored, both theoretically and experimentally, to form a variety of functional materials for application in various fields of chemistry, biology, and polymer and nanomaterials science. We show, using the MESP model, that these highly-valued delocalized systems feature electron-rich and electron-deficient π-regions that can be regarded as negative and positive π-holes, respectively. The former and latter may be regarded as efficient π-hole acceptors of electrophiles (viz. a hydrogen bond) and tetrel bond donors, respectively, when in close proximity with the same or different chemical systems in the crystalline phase. The appearance of negative regions on the surface of the CC bonding region of the chemical systems considered for investigation was found to be consistent with the relatively large delocalization index of the corresponding bond, revealed using the quantum theory of atoms in molecules. Some dimers of C₂₀, C₆₀ and C₇₀ fullerene systems with commonly known diatomic molecules (N₂, CO, HX and X₂ (X = F, Cl, Br) and F₂, etc.) are investigated to illustrate the concept developed above.