An Anomalous Endohedral Structure of Eu@C₈₂ Metallofullerenes

Abstract

Trivalent metallofullerenes such as La@C 82 and Ce@C 82 , in which the metal ions prefer to take a trivalent charge state, have been extensively investigated.[1] However, studies on metallofullerenes encapsulating divalent Sm, Eu, Tm, and Yb metal ions have been limited because of the known low yields in the production of these metallofullerenes despite the development of some improved production and extraction methods during the past several years.[2] This situation has resulted in the structures of such metallofullerenes not having been studied in detail. The variety of encaged metal ions and charge transfer as well as the movement of entrapped metal ions are expected to provide different physical properties. Therefore, it is necessary to study the structure and electronic properties of metallofullerenes in this divalent group.The Eu ion in Eu@C 82 was shown by experiment to transfer two electrons to the fullerene cage.[2c] There are no unpaired electrons on the Eu@C 82 cage and charge transfer results in the 4f 7 5d 0 6s 0 electronic configuration, which gives rise to the fullerene having paramagnetic character. It is thus difficult to determine the structure of the cage and the symmetry of the complex by NMR spectroscopy. XRD measurements have become the only way to access the detailed structure of Eu@C 82 fullerenes.X-ray analysis performed using a combination of the maximum entropy method (MEM) and Rietveld refinement (the MEM/Rietveld method [3] ) has proven to be a powerful method for the accurate determination of the structures of metallofullerenes. The endohedral nature of a series of metallofullerenes, such as La, Y, Sc, and Gd@C 82 , [4] Sc 3 @C 82 , La 2 @C 80 , Sc 2 @C 84 , Sc 2 @C 66 , and Sc 2 C 2 @C 84 [5] has been determined successfully by this method.In the present study the structures of the two isomers of Eu@C 82 (I, III) were successfully determined by the MEM/ Rietveld method using synchrotron X-ray powder diffraction data. The endohedral structure of Eu@C 82 (III) is exceptional in view of the fact that the Eu ion is adjacent to the C À C double bond on the C 2 axis of the C 2v carbon cage, whereas the metal ions (such as La, Y, Sc, Er, Lu) in the normal monometallofullerenes are adjacent to a hexagon of the C 82 cage, except for Gd@C 82 . [4d, 6] Similar to previous studies of La-, Y-, Sc-, and Gd@C 82 , [4] Sc 3 @C 82 ,[5a] La 2 @C 80 , [5b] as well as Sc 2 @C 84 , [5c] the Eu@C 82 (I, III) crystals are assigned to monoclinic P2 1 (no. 4) space groups from the peak positions of the Bragg reflections. The lattice parameters for both isomers are slightly different from each other, namely, a = 18.2870(4), b = 11.2381(2), c = 11.2371(2) , b = 107.769(3)8 for isomer I of Eu@C 82 and a = 18.3143(5), b = 11.2478(2), c = 11.2308(3) , and b = 107.706(3)8 for isomer III.The experimental data were analyzed by the MEM/ Rietveld method.[3] The reliability factors of the final Rietveld refinement for Eu@C 82 (I and III) are R I = 4.58 % and R wp = 2.64 % and R I = 4.57 % and R wp = 1.79 %,...

Co‐operative Formation of Monolithic Tungsten Oxide–Polybenzylene Hybrids via Polymerization of Benzyl Alcohol and Study of the Catalytic Activity of the Tungsten Oxide Nanoparticles

“…In contrast to most of the known endohedral Zintl anions, there is no need to form a deltahedral cage to handle an electron deficit according to Wade–Mingos rules 20. The formal +II oxidation state at the interstitial atom is further supported by the same situation being observed in Eu@C 82 , for example 21. Other Ln ions, such as La and Ce, encapsulated in this carbon cage prefer the trivalent state 10…”

Recent Advances in Rare‐Earth Polypnictides

“…In contrast to the [Eu@Sn 6 Bi 8 ] 4– anion, the rare earth cations in these clusters retained their formally +3 oxidation state as in the precursor. This observation of oxidation states in such clusters is in accordance with that known for La@C 82 , Ce@C 82 and Eu@C 82 …”

[Eu@Sn6Bi8]4−: A Mini‐Fullerane‐Type Zintl Anion Containing a Lanthanide Ion

“…[21] Other Ln ions, such as La and Ce, encapsulated in this carbon cage prefer the trivalent state. [10] With exclusively non-deltahedral faces, the structural features of the anion in 1 are related to those of fullerenes.…”