Endohedral Complexes of Fullerenes

AC and AEC complexation is also effected efficiently by other macrocyclic ligands such as the spherands 13, cryptospherands 14 [2.9, 2.10], calixarenes [2.38, A.6, A.23], torands [2.39], etc., some of them, for instance the spherands displaying particularly high stabilities. A special case is represented by the endohedral complexes of fullerenes in which the cation (Sr2, Ba2+, lanthanides) is locked inside the closed carbon framework [2.40],... 

Interaction-induced spectra of endohedral complexes of buckminster-fullerene. p. 261, 1995. In Ref. [9]. 

The endohedral fullerenes U C28 and U C6o have been reported to be sufficiently stable to allow chemical isolation. Endohedral complexes of the smaller fullerenes (C2 , 2n < 60) are conunonly observed in molecular beam experiments (Section 4.1), but this stabilization of C28 by uranium atom encapsulation is remarkable. A theoretical study of [7i-C28]" and Td-C2iiU (25) indicate that they are stable molecules, and that the laboratory preparation of their derivatives may be viable. ... 

Since the concept of endohedral fullerenes is important in the context of the current presentation, the CPK structure of C50 is presented in figure 1 next to the structure of a cryptate, in this case the lanthanum complex of tris-bipyridyl cryptand, [La(bipy)3]. For the sake of the argument being presented here, assume that the 60 is really an endohedral complex of some metallic ion or ions. 

Cso peapods, C50 encapsulated inside a CNT, were first produced and observed during CNT synthesis by pulsed laser vaporization [150]. Nowadays the synthesis of encapsulated fullerenes [151], endohedral fullerenes [71,151-156] and volatile organometallic complexes of fullerenes [157] within the CNTs is mainly achieved by vapor phase filling technique, consisting in heating at the... 

Computational approaches are now becoming powerful complementary methods to experimental techniques and I am particularly pleased that I have been able to persuade five authors to contribute chapters detailing the applications of these methods to calixarenes and their complexes, to clathrate hydrates, to cyclodextrins and their complexes, to crown ether complexes, to zeolites and their complexes, and to endohedral complexes of the intriguing fullerene molecules. 

Hesseimann A, Korona T (2011) On the accuracy of DFT-SAPT, MP2, SCS-MP2, MP2C, and DFT plus Disp methods for the interaction energies of endohedral complexes of the Cgo fullerene with a rare gas atom. Phys Chem Chem Phys 13 732-743... 

Y. Rubin, Ring Opening Reactions of Fullerenes Designed Approaches to Endohedral Metal Complexes , Top. Curr. Chem. 1999,199, 67-91. 

Crystal structures of a few fullerenes containing endohedral atoms have been recently solved (apart from the noble gas trapping Kr C60,22a the metal atoms containing Sc3 N C78,22b Sc3 N C80 and Sc2 ErN C80>22c Y C82,22d Sc C82,22e Er2 C82,22f Sc3 Cs2,228 Sc2 C84,22h Sc2 C2 C84,221), but unfortunately their electrochemical behaviour is not known. Electrochemical information is also limited for those endohedral complexes which lack definitive structural characterization.23... 

One of the most remarkable properties of fullerenes is their ability to encapsulate atoms, ions and small molecules, to form the so-called endohedral fullerene complexes, denoted... 

For the first time the small fullerene molecule C28 was discovered in structure of endohedral complex U C28 [11]. The entire first attempts to extract the isolated molecule C28 in purely kind failed. Theoretical calculations show that isolated molecule C2g is radical with 4 non-paired electrons (S = 2), localized on atoms, disposed in vertexes which are common for each three neighboring pentagons. Exactly this fact explains the high activity of isolated molecule C28 and unsuccessful attempts to get it in purely kind. 

In this chapter on chemically modified fullerenes, I will discuss only a few representative molecules which incorporate fullerenes, and focus attention on the best-characterized compounds. A comprehensive review of chemical reactions with fullerenes has just been published by Taylor and Walton.[Ta93] It is not appropriate here to attempt a synthesis of the emerging field of the chemical properties of the fullerenes. Covered elsewhere in this book are ioni-cally bonded fullerides, such as the superconductor KsCeo (Chapter IV) and endohedral complexes, in which various atoms are captured inside the hollow carbon shell (Chapter VI). 

Another remarkable endohedral complex which, has recently been created is U C2s.[Gu92] This affords a counterexample to the observation that endohedral complexes are typically based on fullerenes larger than Ceo- Indeed, C28 appears to be the smallest fullerene produced in supersonic cluster beams from a laser-vaporization source. Photofragmentation experiments ve an additional sense of how strongly the internal U stabilizes C28- Larger, empty fullerenes can be blasted down to C32, but... 

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