Substitution effects via aromaticity, polarizability, APT, AIM, IR analysis, and hydrogen adsorption in C20-nTin nanostructures: a DFT survey.

In this paper, the substitution effects of titanium heteroatom(s) on aromaticity, the average isotropic polarizability (< α >), the atomic polar tensor (APT) charge, the electrostatic potential (ESP) map, and the atoms in molecule (AIM) analysis along with infrared (IR) spectroscopy of C20 fullerene and its C20-nTin derivatives (n = 1-5) are probed via density functional theory (DFT). The nucleus-independent chemical shifts (NICS) specify that substitution effect causes more aromaticity character of the optimized heterofullerenes than benzene molecule and higher APT charge distribution upon surfaces of them than pure cage. The highest negative and positive APT charge distribution on carbons of C15Ti5 and titanium substitutions of C16Ti4-2 implies that these sites can be attacked more readily by electrophilic and nucleophilic regents, respectively. We are very pleased to state that isolating the Ti-Ti single bonds by intermediacy of one or two C atoms is an applicable strategy for attaining the highest APT charge distribution on Ti atoms of C16Ti4-2 as suitable hydrogen storage. AIM analysis of the studied C20-nAln derivatives signifies the highest electron density (ρ (r)) of 0.294 a.u. and the highest positive Laplacian of electron density (∇2ρ (r)) of 0.190 a.u., at bond critical points (BCPs) of C-Ti bond in the most stable C19Ti1 species. This heterofullerene shows the lowest < α > between the studied structures. IR spectroscopy shows that exclusive of C16Ti4-1 (as transition state), the other optimized hollow cages (as global minima) have no imaginary frequency.