Enhanced localization of tunneling of the NH3 umbrella mode in nano-cage fullerene

The Acid-Base Through-the-Cage Interaction as an Example of an Inversion in a Cage Isomerism

We define a new inversion in a cage isomerism (ic): X@C⋯Y₪icY@C⋯X, (₪ is the isomerism relation) as an isomerism in the three-component system of molecules X, Y, and a cage C, in which one of the molecules is located inside and the other outside the cage. The ic isomerism is similar to the endo-exo one, which occurs only if either the interior or exterior of C is empty. By contrast, ic occurs only if neither the interior nor the exterior of C is empty. We also discuss the other closely related types of isomerisms are also discussed. Calculations of the XH⋯NH3@C60 and NH3⋯HX@C60ic isomers were performed at the ωB97XD/Def2TZVP level. The calculated energies demonstrated that the systems with the HX acid outside (X = F, Cl) and the NH3 base inside the cage, XH⋯NH3@C60, are more stable than their ic isomers, NH3⋯HX@C60, by about 4–8 kcal/mol. This is because NH3 is more stabilized inside the cage than HX (a matter of 6.5 kcal/mol). In the studied systems and subsystems, the HX molecules are Lewis acids and the NH3 molecule is always a Lewis base. The C60 molecule with HX inside or outside the cage is also an acid for the NH3 base positioned outside or inside the cage. On the other hand, the C60 cage is truly amphoteric because it is simultaneously an acid and a base.

Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including -COOX (X=H, CH3, CH2NH2, CH3Ph, CH2NO2, and CH2CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of -0.23 to -7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is -CH2NO2>-CH2CN>-H>-CH2Ph>-CH3>-CH2NH2. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for -H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of -CH2NO2 and -CH2CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.