A theoretical study of spin density distributions and isotropic hyperfine couplings of N and P atoms in N@C60, P@C60, N@C70, N@C60(CH2)6, and N@C60(SiH2)6

Spin density distributions and isotropic hyperfine coupling constants of N@C60, P@C60, N@C70, N@C60(CH2)6, and N@C60(SiH2)6 are theoretically investigated by testing B3LYP and MP2 methods for the free N and P atoms. When N is encapsulated inside C60, the calculated spin density at nucleus N increases. In P@C60, the corresponding increase is much larger. N@C60 has a slightly larger spin density at N than N@C70. These agree well with the observed isotropic hyperfine coupling constants. Upon addition of CH2 groups on the N@C60 cage, the spin density at N is slightly decreased. However, addition of SiH2 groups increases significantly the spin density at the nitrogen nucleus.