Single Samarium Atoms in Large Fullerene Cages. Characterization of Two Isomers of Sm@C92 and Four Isomers of Sm@C94 with the X-ray Crystallographic Identification of Sm@C

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• 作者：Hongxiao Jin ; Hua Yang ; Meilan Yu ; Ziyang Liu ; Christine M. Beavers ; Marilyn M. Olmstead ; Alan L. Balch
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：July 4, 2012
• 年：2012
• 卷：134
• 期：26
• 页码：10933-10941
• 全文大小：630K
• 年卷期：v.134,no.26(July 4, 2012)
• ISSN：1520-5126

文摘

Two isomers of Sm@C₉₂ and four isomers of Sm@C₉₄ were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm₂O₃. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni^II(octaethylporphyrin) reveals the identities of two of the Sm@C₉₂ isomers: Sm@C₉₂(I), which is the more abundant isomer, is Sm@C₁(42)-C₉₂, and Sm@C₉₂(II) is Sm@C_s(24)-C₉₂. The structure of the most abundant form of the four isomers of Sm@C₉₄, Sm@C₉₄(I), is Sm@C_3v(134)-C₉₄, which utilizes the same cage isomer as the previously known Ca@C_3v(134)-C₉₄ and Tm@C_3v(134)-C₉₄. All of the structurally characterized isomers obey the isolated pentagon rule. While the four Sm@C₉₀ and five isomers of Sm@C₈₄ belong to common isomerization maps that allow these isomers to be interconverted through Stone鈥揥ales transformations, Sm@C₁(42)-C₉₂ and Sm@C_s(24)-C₉₂ are not related to each other by any set of Stone鈥揥ales transformations. UV鈥搗is鈥揘IR spectroscopy and computational studies indicate that Sm@C₁(42)-C₉₂ is more stable than Sm@C_s(24)-C₉₂ but possesses a smaller HOMO鈥揕UMO gap. While the electronic structures of these endohedrals can be formally described as Sm²⁺@C_2n^{2鈥?/sup>, the net charge transferred to the cage is less than two due to some back-donation of electrons from 蟺 orbitals of the cage to the metal ion.}