Multiple Addition of Methylamine to Fullerene C60: A Density Functional Theory Study
Abstract:By means of density functional theory calculations at the PW91/DN theoretical level, we performed a systematic analysis of possible nucleophilic addition sites of one to six methylamine molecules onto fullerene C60. Particular questions we addressed, using the formation energy as a thermodynamic criterion of reactivity, were whether the 6,6 C=C bonds of pyracylene units remain always the preferential addition sites at every amination step, and whether the carbon atoms with larger pyramidalization angles p play a relevant role for the addition regioselectivity. By comparing the energies of formation of different isomeric products, we found that the most favorable additions are observed on the 6,6 C=C bonds, and never on the 5,6 junctions. Furthermore, a preferable polyaddition pattern is the one where –NHCH3 and –H addends form an aligned chain, with the carbon atoms to which they are attached alternating in a zigzag order. As a whole, no direct correlation between the pyramidalization angle p and reactivity was found. An analysis of the plots of formation energy versus the initial (before addition) 6,6 bond length showed that the preferential additions are those onto relatively short C=C bonds of about 1.380–1.390 Å long, but not on the shortest bonds of ca. 1.370 to 1.375 Å. The latter cases are associated with a considerable steric hindrance due to the addition of three methylamine units to one hexagon of C60, as well as with the smallest values of pyramidalization angles at the site of the third CH3NH2 addition.
Document Type: Research Article
Publication date: January 1, 2009
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