Atomic nitrogen in C60:N@C60

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(atomic nitrogen inside C₆₀) is produced by ion implantation. Two different production methods are employed: Kaufman ion source and glow discharge. After the bombarded material is dissolved in toluene or CS₂ and is filtered, several milligrams of C₆₀ containing N@C₆₀ in a concentration of 10^-4 to 10^-5 are obtained. N@C₆₀ gives a very clear hyperfine-split electron paramagnetic resonance signal. The most prominent features of N@C₆₀ are: (i) Nitrogen in C₆₀ keeps its atomic electronic configuration and occupies the on-center position. (ii) N@C₆₀ is stable at ambient conditions, the thermal instability starts at 260 °C. (iii) The complex survives exohedral addition reactions and is a sensitive detector of cage distortions caused by addends. (iv) C₆₀ and N@C₆₀ exhibit slightly different retention times in column chromatography, thus permitting an enrichment of N@C₆₀ by this method.