Nondestructive Quantitative Analysis of Lithium Ion-Endohedral Fullerene Salt (Li ⁺ @C ₆₀ ·PF ₆ ^– ) via ¹⁹ F NMR Spectroscopy

A quantitative analysis of the lithium ion-endohedral fullerene salt, Li⁺@C₆₀·PF₆ ^- (<b>1</b>), was performed using ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. To establish a robust quantitative ¹⁹F NMR (qNMR) method, experimental parametersincluding spin-lattice relaxation time (<i>T</i> ₁), relaxation delay, and offset frequencywere optimized using tetrabutylammonium hexafluorophosphate (TBA⁺·PF₆ ^-) as a model compound and α,α,α-trifluorotoluene (PhCF₃) as an internal standard. The purity of <b>1</b> was determined using a calibration curve constructed from ¹⁹F NMR measurements, which effectively minimized systematic errors. The purity value obtained via this nondestructive qNMR method was approximately 95%, showing excellent agreement with quantitative results obtained from inductively coupled plasma atomic emission spectroscopy (95.1%). This method offers a rapid, specific, and nondestructive alternative for the purity evaluation of endohedral metallofullerenes allowing for complete sample recovery.