¹⁵N 同位素标记的金属氮化物内嵌富勒烯的合成与表征

In this work, we prepared the ¹⁵N-labeled metal nitride clusterfullerene by arc discharge method. In the synthetic process, scandium metal, graphite powder, and ¹⁵NH₄Cl were atomized by arc discharge method under helium atmosphere with ¹⁵NH₄Cl as solid nitrogen source, and finally Sc₃¹⁵N@C₈₀ and Sc₃¹⁵N@C₇₈ were obtained. Sc₃¹⁵N@C₈₀ was isolated by high-performance liquid chromatography (HPLC) and characterized by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, UV-Vis absorption spectra, and ¹³C NMR. These results demonstrate the successful labeling of ¹⁵N and also illustrate that the prepared Sc₃¹⁵N@C₈₀ has an I_h-C₈₀ cage. The prepared ¹⁵N-labeled metal nitride clusterfullerenes contain more than 98% of the ¹⁵N isotope, which will expand the application fields of metallofullerene materials such as isotope tracing. In detail, clusterfullerenes were separated from hollow fullerenes by multistage HPLC. And then pure samples of Sc₃¹⁵N@C₈₀-I_h and Sc₃¹⁵N@C₇₈ were obtained. Mass spectrometry was used to characterize the molecular weight of Sc₃¹⁵N@C₈₀-I_h and Sc₃¹⁵N@C₇₈. According to the isotopic distributions of Sc₃¹⁵N@C₈₀-I_h and Sc₃¹⁵N@C₇₈ in mass spectra, their molecular weight values have increased by 1 compared to those of unlabeled Sc₃N@C₈₀-I_h and Sc₃N@C₇₈, revealing the successful labeling of isotope ¹⁵N on the Sc₃N cluster. At the same time, we added Y₃N@C₈₀ as an internal standard into Sc₃¹⁵N@C₈₀-I_h and Sc₃¹⁵N@C₇₈ samples to further confirm the labeling of ¹⁵N atom on the Sc₃N cluster. Moreover, the UV-Vis absorption spectrum showed that the absorption of Sc₃¹⁵N@C₈₀ begins at 820 nm, and the lowest energy transition was observed at 735 nm. Based on the absorption onset, the optical energy gap of Sc₃¹⁵N@C₈₀ can be calculated, which is about 1.51 eV. According to the reported UV-Vis absorption spectra in literature, the carbon cage of the isolated Sc₃¹⁵N@C₈₀ can be characterized as I_h-symmetry. The carbon nuclear magnetic resonance spectroscopy (¹³C NMR) was executed by dissolving Sc₃¹⁵N@C₈₀ in 1, 2-dichlorobenzene-d₄ at 293 K. The ¹³C NMR spectrum consists of only two NMR lines of chemical shifts of 143.60 and 136.37 with an intensity ratio of 3:1. This is a characteristic ¹³C NMR spectrum of the I_h-symmetric C₈₀ carbon cage.