Confirmation of a vanishingly small ring-current magnetic susceptibility of icosahedral C₆₀

In 1987, Elser and Haddon predicted a vanishingly small π-electron contribution to the magnetic susceptibility of the icosahedral C₆₀ molecule (buckminsterfullerene). This result runs counter to intuition and was subsequently disputed on the basis of ab initio computations. Following the recent discovery of methods for preparing (and purifying) large quantities of C₆₀, we here report measurements of the magnetic susceptibility, χ, of a solid sample of pure C₆₀ by SQUID magnetometry. The obtained mass value, χ_g = -0.35 × 10^-6, is far below that of graphite or benzene, consistent with the Elser-Haddon picture of accidental cancellation of the diamagnetic and paramagnetic contributions to χ. An estimate of the unusually large paramagnetic contribution is in accord with recent measurements of C₆₀'s electronic excitations. The C₇₀ molecule is also measured to have χ_g = -(0.59 ± 0.05) × 10^-6.