Synthesis and Characterizations of 15N Isotope Labeling Metal Nitride Clusterfullerene

In this work, we prepared the N-15-labeled metal nitride clusterfullerene by arc discharge method. In the synthetic process, scandium metal, graphite powder, and (NH4Cl)-N-15 were atomized by arc discharge method under helium atmosphere with (NH4Cl)-N-15 as solid nitrogen source, and finally (Sc3N)-N-15@C-80 and (Sc3N)-N-15@C-78 were obtained. (Sc15N)-N-3@C-80 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 C-13 NMR. These results demonstrate the successful labeling of N-15 and also illustrate that the prepared (Sc3N)-N-15@C-80 has an Ih-C-80 cage. The prepared N-15-labeled metal nitride clusterfullerenes contain more than 98% of the N-15 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 (Sc3N)-N-15@C-80-Ih and (Sc3N)-N-15@C-78 were obtained. Mass spectrometry was used to characterize the molecular weight of (Sc3N)-N-15@C-80-I-h and (Sc3N)-N-15@C-78. According to the isotopic distributions of (Sc3N)-N-15@C-80-Ih and (Sc15N)-N-3@C-78 in mass spectra, their molecular weight values have increased by 1 compared to those of unlabeled Sc3N@C-80-I-h and (ScN)-N-3@C-78, revealing the successful labeling of isotope N-15 on the Sc3N cluster. At the same time, we added Y3N@C-80 as an internal standard into (Sc3N)-N-15@C-80-I-h and Sc315N@C78 samples to further confirm the labeling of N-15 atom on the Sc3N cluster. Moreover, the UV-Vis absorption spectrum showed that the absorption of (Sc3N)-N-15@C-80 begins at 820 nm, and the lowest energy transition was observed at 735 nm. Based on the absorption onset, the optical energy gap of (Sc3N)-N-15@C-80 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 (Sc3N)-N-15@C-80 can be characterized as Ih-symmetry. The carbon nuclear magnetic resonance spectroscopy (C-13 NMR) was executed by dissolving (Sc3N)-N-15@C-80 in 1,2-dichlorobenzene-d(4) at 293 K. The C-13 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 C-13 NMR spectrum of the Ih-symmetric C-80 carbon cage.

Automated summary

In this study, N-15-labeled metal nitride clusterfullerenes were successfully prepared, demonstrating potential applications for metallofullerene materials.