Endohedral Metallofullerene M2@C80: A New Class of Magnetic Superhalogen

Superhalogen is a special class of atomic clusters whose electron affinity is larger than that of chlorine atom, which has the largest electron affinity in the periodic table of elements. In this paper, we report the fabrication of a new class of magnetic superhalogen by encapsulating two rare-earth metal atoms into the I h symmetrical C80 fullerene. The as-produced metallofullerene has an electronic configuration of M2 5+@C80 5–. The addition of an extra electron to the molecule leads to the formation of a highly stable structure M2 5+@C80 6–. Density functional theory calculations reveal that M2@C80 has a larger electron affinity than the chlorine atom. Thus, M2@C80 can be classified as superhalogen. The magnetic properties of the M2@C80 superhalogens are associated with the single-electron metal–metal molecular orbital and the partially filled f electron shell of the metal atoms. Electron spin resonance measurement discloses the paramagnetic character of Y2@C80 – and the strong coupling effect between the unpaired electron and the Y nuclei. The outer fullerene cage provides a suitable environment for protecting the unconventional valence and spin states of the inner metal atoms. A variety of superhalogens with distinct magnetic properties can be obtained by encapsulating different lanthanide metal atoms into the C80 fullerene. Such superhalogens can serve as building blocks of materials with tailored magnetic properties.