Ab initio and density functional study on fullerene C44 and its derivatives

The 89 classical C44 isomers, its anions and derivatives such as C44Xn (X = H, F, and Cl; n = 14 and 16) and M@C44 (M = He, Li, and Ca) have been systematically investigated by ab initio and density function methods. Although the D2:75 species has the least number of adjacent pentagons, the MP2 geometry optimizations suggest that the D3h:72 structure is favored by ∼11 kcal/mol over the D2:75 isomer. Systematic investigations of the electronic properties show that neutral D3h:72 is highly aromatic. In contrast, the two lowest energy isomers of C 44 2 - , D2:75 and D2:89, are highly aromatic. Compared with C50X10 (D5h), the large energy gaps and the aromatic character of C44X14 (D3h:72) indicate that they possess high stabilities. Furthermore, the predicted reaction energies of C44X14 (D3h:72) derivatives are highly exothermic, suggesting a considerable possibility for experimental realization. Investigations also show that the D2:75 endohedral structure is most stable for Ca@C44.