Electron Spin Manipulation via Encaged Cluster : Di ff ering Anion

Endohedral metallofullerene species with controllable electron spin have attracted increasing attention along with their potential application in quantum information processing. In this paper, we report the electron spin manipulation via encage cluster through comparative studies on the anion radicals of metallofullerene Y2@C82-Cs, Y2C2@ C82-Cs, and Sc2C2@C82-Cs. Although these three radical species have the same parent fullerene cage, we found that the unpaired spin characteristics as well as metal-spin couplings of them can be greatly affected by endohedral clusters. Furthermore, based on theoretical calculations, it was revealed that the encaged clusters can affect the electronic population of pristine endohedral metallofullerenes and eventually manipulate the spin distribution of their corresponding anion radicals. Our findings are referential to the spin coherence in information processing due to the variable paramagnetism of these metallofullerene radicals. SECTION: Molecular Structure, Quantum Chemistry, and General Theory E metallofullerenes are constructed by fullerene cages encapsulating metal ions or clusters, and their unique structures have brought many novel physical and chemical properties. For example, some endohedral metallofullerene radicals, e.g., Sc@C82, Y@C82, Sc3C2@C80 etc., show extremely high stability due to the delocalized or even embedded unpaired spin by the fullerene cages. Recently, along with the rapid progresses on quantum information processing and quantum computing, the manipulation of electron spin has become a hot subject; thus, endohedral metallofullerene radicals with stable and controllable electron spins will have important application prospects. In general, the manipulation of electron spin on a paramagnetic metallofullerene involves the electron spin distribution on fullerene molecules, the interaction between the fullerene cage and internal species, the couplings between the metal nuclei and unpaired spin, and the thermal rotation of the internal species, etc. In order to explore how the electron spin distributions were manipulated by the endohedral species, here three endohedral metallofullerenes Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs with the same parent fullerene cage were chosen, and a comparison study on their radical properties was performed. Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs samples were prepared by the Kraẗschmer−Huffman arc discharging method and isolated by high-performance liquid chromatography (HPLC). The purity of the three samples was confirmed by both the HPLC analysis and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (see Supporting Information (SI)). Since the structures of Y2@ C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs molecules have been characterized by single crystal X-ray analysis and NMR method in literature, here only comparative Raman and ultraviolet/visible−near infrared (UV/vis−NIR) absorption spectroscopic studies on them were performed (see SI). It was revealed that the UV/vis-NIR absorption spectra of Y2@C82, Y2C2@C82, and Sc2C2@C82 resemble each other, and show similar spectral features with the related literature. As for Raman spectroscopy, the three molecules exhibit analogous spectral features in the region between 1000 and 1600 cm−1, corresponding to the C82-Cs cage tangential vibrations, and quite large difference in the region between 100 and 600 cm−1, corresponding to the vibrations from different encaged clusters. The anion radicals of Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@ C82-Cs were prepared by contacting potassium metal with the samples in tetrahydrofuran (THF) solution several times under nitrogen atmosphere. Then the resulting anion radicals were measured by electron spin resonance (ESR) spectroscopy with continuous Xband wave at room temperature. The ESR spectra of the Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs anion radicals were successfully obtained shown in Figure 1. For Y2@C82-Cs anion radical, the ESR spectrum Received: December 12, 2012 Accepted: January 15, 2013 Letter