Theoretical studies on the proton affinities of four different series of nano-size diamines and designing strong superbases based on fullerene(C60) molecule

Abstract

Density functional theory (B3LYP) calculation is used to determine the gas-phase proton affinities of four series of nano-size diamines (1–2.3 nm) including –(CH₂)_n–C₆₀–(CH₂)_n–, –(C₆H₄)_n–, –(CHCH)_n–, and –(CH₂)_n– spacers, where the maximum value of n is 5, 5, 9 and 15, respectively. The results showed that, in the case of diamines with two former spacers the first proton affinity, PA₁, decreases by increasing the value of n, while in the case of two latter diamines it increases by increasing the value of n. However, the second proton affinity, PA₂, and proton overallaffinity, PA_ov, of all above molecules, as expected, increases with increasing the value of n. Among all above compounds the greatest amounts of the PA₁ and PA₂ were calculated for H₂NCH₂–C₆₀–CH₂NH₂ and H₂N–(CH₂)₁₅–NH₂ molecules, respectively. It seems that the C₆₀ molecule has an increasing effect on PA₁ of diamines, while a saturated long aliphatic chain which separates well the positively charged nitrogen atoms has an increasing effect on PA₂ of diamines. The above results has led us to design new nano-size superbases with –N(CH₃)₂ or –NC{N(CH₃)₂}₂ basic groups on fullerene molecule. The amounts of PA₁, PA₂ and PA_ov, for one of these superbases are 1126.3, 786.6 and 1912.9 kJ mol⁻¹, respectively, indicating that it is one of the strongest superbases known so far.