Preparation of endohedral fullerene containing lithium (Li@C60) and isolation as pure hexafluorophosphate salt ([Li+@C60][PF6−])
A synthetic protocol for endohedral fullerene containing lithium (Li@C60), as well as the synthesis, characterization, and properties of its chemically oxidized derivative [Li+@C60][PF6−] are reported in full. Simultaneous deposition of Li plasma and C60 produces a mixture containing Li@C60 and C60. Strong intermolecular attraction between Li@C60 and C60 has prevented their separation, but this obstacle was surmounted by selective chemical oxidation of Li@C60, which led to the isolation of a substantial amount of pure [Li+@C60][PF6−]. For this purpose, an HPLC technique using an electrolyte in the mobile phase was effective in purifying the ionic metallofullerene. [Li+@C60][PF6−] was stable in air and, compared with [Li+@C60][SbCl6−], was more stable to moisture and various chemicals. [Li+@C60][PF6−] holds promise for practical applications. The spectroscopic data (MS, 7Li and 13C NMR, UV-vis, and IR) and electrochemical data for [Li+@C60][PF6−] are disclosed. In addition, the high electron affinity of [Li+@C60][PF6−] is discussed.