• PDF / 1,795,818 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 83 Downloads / 182 Views

DOWNLOAD

REPORT

---

1204-K10-20

Investigation of Gd2@C90, Gd2C2@C92, and Gd2@C79N by Raman Spectroscopy Brian G. Burke1,*, Tsz-Wah (Jack) Chan1, Keith A. Williams1, Jiechao Ge2, Chunying Shu2, Wujun Fu2, Harry C. Dorn2, Alexander Puretzky3, and David Geohegan3 1 Department of Physics, University of Virginia, Charlottesville, Virginia 22903, U.S.A. 2 Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, U.S.A. 3 Materials Science and Technology Division, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, U.S.A.

ABSTRACT The structure and vibrational spectrum of Gd2 and Gd2C2 endofullerenes are studied through Raman spectroscopy and universal force field (UFF) calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd–cage bond, which reduces the ideal symmetry of the cage. We have conducted Raman studies of Gd2@C90, Gd2@C79N, and Gd2C2@C92. We have also studied Y2C2@C92 for comparison. Several modes have been identified which provide information about the endohedral complex.

INTRODUCTION Endohedral fullerenes (endofullerenes), due to their unique electronic and geometric structure, have been attracting the interest of chemists, physicists, and material scientists since they were first synthesized in 1985 [1]. Fullerenes can act as hosts that encapsulate other atoms, molecules, or atomic clusters. The resulting endofullerenes have initiated considerable research because the entrapped atoms bring with them an array of useful physical properties, such as electronic devices [2], organic solar cells [3], spin-based quantum computing [4,5], and medical applications [6,7]. Additionally, the fullerene cage acts to protect the interior metal atoms and can provide ways of maintaining selected properties of the metallic clusters while the endofullerene is functionalized with ligands or organized in cluster assemblies. Endofullerenes created by an arc-vaporization technique have been known to encapsulate magnetic or radioactive metal atoms, which have made a huge impact in interdisciplinary areas like biology and medicine. Endofullerenes containing gadolinium are particularly important, since they may contribute to the development of second generation relaxation agents for magnetic resonance imaging (MRI) as well as radiopharmaceutical candidates in nuclear medicine [8]. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the metal complex. Based on the mode frequencies, the experimental value of the metal–cage bond strength can be determined and the amount of charge transfer from the cage to the core can be investigated [9-11]. It has been shown that some isolated fullerene cages, though electronically unstable, can bind strongly to the metal core and become stable [12].

In this paper, we present a detailed Raman analysis of Gd2@C90, Gd2@C79N, and Gd2C2@C92. Vibrational assignments of the intrinsic core complexes