Actinide Nitride Clusterfullerene: Synthesis, Isolation and Spectroscopic Characterization of U2N@C80

Abstract

All the nitride clusterfullerenes discovered so far adopted a trimetallic nitride template. Here, we report that an unprecedented nitride cluster endohedral fullerene with only two metal atoms in the cluster, U2N@C80, has been successfully synthesized by a modified arc-discharge method and isolated by a multistage HPLC process. Mass spectroscopy, UV-vis-NIR absorption spectrometry and Raman spectroscopy were employed to investigate its structure and some intriguing properties have been revealed. The UV-vis-NIR absorption spectrum of U2N@C80 in CS2 is featured with two weak absorption peaks at 446nm and 680 nm. Compared with previously reported M3N@I h(7)-C80 (M= Tm, Gd, Y, Er, Dy) fullerenes, their overall absorption spectra, characteristic absorption peaks and optical band gaps are almost identical, providing evidence for a probable six-electron transfer from the interior cluster to the exterior fullerene cage. In addition, the features of the low energy Raman spectrum of U2N@C80 also show similarities to those of fullerenes with I h-C80 cage, which agree well with the UV-vis-NIR absorption study. However, in the range of 100-200 cm‒1, the peaks of the stretching metal-cage mode is observed at 119,135 cm‒1, which shows great difference from those of lanthanide endohedral fullerenes, M3N@I h(7)-C80 (M=Tm, Gd, Y, Er, Dy), indicating a quite different metal-to-cage interaction between the inner cluster and the I h(7)-C80 cage from that of the lanthanide nitride endohedral fullerenes.