Preparation of endohedral fullerene containing lithium (Li@C₆₀) and isolation as pure hexafluorophosphate salt ([Li⁺@C ₆₀][PF₆^-])

A synthetic protocol for endohedral fullerene containing lithium (Li@C ₆₀), as well as the synthesis, characterization, and properties of its chemically oxidized derivative [Li⁺@C₆₀][PF ₆^-] 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][PF ₆^-]. 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][SbCl ₆^-], 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][PF ₆^-] is discussed.