Ab initio helium NMR chemical shifts of endohedral fullerene compounds He@C_n (n = 32−180)

Helium NMR chemical shifts have been computed at the gauge including atomic orbitals (GIAO)-SCF/dz(C), tzp(He)//MNDO level for the endohedral fullerene compounds He@C_n (n = 32, 36, 50, 60, 70, 76, 78, 80, 82, 120, 180). The endohedral He shielding increases in the sequence C₆₀ < C₈₄ < C₈₂ < C₇₈ < C₇₆ < C₇₀, in accord with recent London calculations. For the smaller fullerenes (n < 60), large endohedral shieldings are computed, e.g. δ(He) = −30.3 ppm for He@C₅₀ (D_5h), while a nearly constant endohedral chemical shift of ≈ −17 ppm is predicted for the symmetric large fullerenes C₁₂₀ and C<sub>180