Crystallographic characterization of ErN@C (2n = 80, 82, 84, 88): the importance of a planar ErN cluster.

A series of Er-based nitride clusterfullerenes (NCFs), ErN@C, have been successfully synthesized and isolated. In particular, ErN@I(7)-C, ErN@D(6)-C, ErN@C(9)-C, ErN@C(51365)-C, and ErN@D(35)-C have been characterized by single-crystal X-ray diffraction (XRD) for the first time. The planar configuration of the inserted ErN cluster is identified unambiguously and the Er-N distances increase in accordance with cage expansion to maintain strong metal-cage interactions. Additionally, the electrochemical properties of the ErN@C series are studied by means of cyclic voltammetry. It is found that the first reduction potentials are roughly similar for all compounds under study, while the first oxidation potentials are cathodically shifted along with the increase of the cage size in the ErN@C (2n = 80, 84, 86, 88) series, leading to a decrease in the corresponding electrochemical band gaps. Nevertheless, for ErN@C(9)-C, a good electron donating ability is manifested by its relatively small first oxidation potential, which results from the relatively higher energy level of the highest occupied molecular orbital. The redox behaviors observed in such ErN-based NCFs may promise their great potential applications in donor-acceptor systems.