Theoretical Study on Phosphorus Substitutionally Doped Fullerenes

Since Karfunkel predicted the stability of azafullerenes by semiempirical calculation, a sustaining effort was paid to quantum-chemical calculation of substitutionally dopped fullerenes. While the N and B hetero-fullerenes are the most known, in the last years Si, Co, Ni, Fe, Rh, Ir dopped C60 have been modeled.4-6 This paper reports semiempirical PM3 calculations of phosphorus substituted fullerenes C60- nPn, n = 1-6. The C by P replacement appears to not dramatically influence the thermal stability of substituted C60 but electronic structure is changed. The degeneracy of HOMO and LUMO levels is reduced or destroyed while the HOMO-LUMO gap is, in some cases, as high as in the parent C60 and consistent with a good kinetic stability. The difference between C and P electronegativity determines the partial positive charge at phosphorus and a negative charge at the neighboring C atoms. The displacement of a number of phosphorus atoms on the same polygon diminishes the positive charge at phosphorus. Angles at phosphorus are larger when phosphorus is on a hexagon. The reverse situation is found for bond length that increases for P-C [5,6] with respect to [6,6] bonds. The bonding energy of P-dopped fullerenes decrease with increasing the number of phosphorus atoms, as the strength of P-C bonds decreases with respect to C-C bonds. From energetic considerations, we can draw the conclusion that phosphorus dopped fullerenes may be stable molecules.