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Electron interaction between encapsulated atoms and p -electrons of fullerene cage

Electron interaction between encapsulated atoms and p -electrons of fullerene cage. Shojun Hino Chiba university, Japan. Today’s talk. Background Alkali metal fullerene complexes Photoelectron spectra of fullerenes Mono-metal encapsulated fullerenes M@C 82

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Electron interaction between encapsulated atoms and p -electrons of fullerene cage

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  1. Electron interaction between encapsulated atoms and p-electrons of fullerene cage Shojun Hino Chiba university, Japan

  2. Today’s talk • Background • Alkali metal fullerene complexes • Photoelectron spectra of fullerenes • Mono-metal encapsulated fullerenes • M@C82 • Multiple atoms encapsulated fullerenes • C82 cage • C78 cage (probably skipped) • Summary

  3. Background • Superconductivity in alkali metal – C60 complex From 18 K( K3C60) to 33K (Cs2RbC60) expectation of high temperature superconductor on higher fullerenes

  4. Alkali (alkali earth) metal C60 complexes • Metallic (superconducting*) phase : A1C60, A3C60* (A = K, Rb, Cs) Ca5C60*, Ba6C60* • Not all electron accepting fullerenes become metallic or superconducting.

  5. As for AxC60, Stable phases : A1C60, A3C60, A4C60, A6C60 MetallicAxC60 complexes A = K, Rb, Cs Semiconductive AxC60 complex A = Li, Na, Mg J.Phys.Chem.Solids 53, 1321

  6. Alkali (alkali earth) metal C60 complexes • Metallic (superconducting*) phase : A1C60, A3C60* (A = K, Rb, Cs) Ca5C60*, Ba6C60* • Not all electron accepting fullerenes become metallic or superconducting. • Electron donation to C60 is the key. • They are unstable to the ambient air !

  7. e- O2, H2O C60- e- A+

  8. Alkali (alkali earth) metal C60 complexes • Metallic (superconducting*) phase : A1C60, A3C60* (A = K, Rb, Cs) Ca5C60*, Ba6C60* • Not all electron accepting fullerenes become metallic or superconducting. • Electron donation to C60 is the key. • They are unstable to the ambient air • Remedy?

  9. Enclosure of donor in the cage C60- O2, H2O Encapsulation of electron donating atom(s) prohibits degrading of donor

  10. Alkali (alkali earth) metal C60 complexes • Metallic (superconducting*) phase : A1C60, A3C60* (A = K, Rb, Cs) Ca5C60*, Ba6C60* • Not all electron accepting fullerenes become metallic or superconducting. • Electron donation to C60 is the key. • They are unstable to the ambient air • Remedy :endohedral metallofullerenes

  11. Metallofullerenes synthesized so far Sc@C82 La@C82

  12. Metallic or semiconducting? UPS spectral onset can tell ! NaxC60 KxC60 AxCn(n > 60) Semiconductor! No observation of the Fermi edge Metals! Clear observation of the Fermi edge Alkali metal higher fullerenes complexes are also Non-metallic !

  13. M@C82

  14. Isolated pentagon rule (IPR) satisfying C82 cages M3+@C823- C2v (major), Cs M2+@C822- C2v, C2 Cs, C3v C2 ×3 Cs×3 C3v×2 No.2 Cs(b) No.3 C2(a) No.1 C2(b) No.4 Cs(c) No.5 C2(c) No.6 Cs(a) No.7 C3v No.9 C2v No.8 C3v

  15. One of the issues on M@C82 • What dominates the electronic structure? • Cage structure ? Or entrapped atom ? • Methods: • Measurement on different cage and on metallofullerenes of different entrapped atomic species

  16. Different cage of M3+@C823-no spectrum has been measured containing the same metal atom. C2v Cs

  17. Spectral shapes differ. Reason? Metal species or cage ? These metallofullerenes except Pr@C82 have the same C2v structure. C2v cage fullerenes give essentially the same spectra. Exception is the upper valence region.

  18. M2+@C822- gives answer Measurement on the isomers containing the same atom Tm@C82 (I),(II), (III) symmetry : Cs, C2, C2v Ca@C82(III), (IV) symmetry : C2, not specified Tm@C82 (II) and Ca@C82 (III) gives the same spectra Not entrapped atom but the cage dominates !

  19. Summary of Mono-metal atom entrapped C82 Principally metallofullerenes with the same C2v cage give essentially the same spectra. That is, Small or no interaction between the fullerene cage and the entrapped atom Difference only in upper band due to the difference in the amount of electrons transferred

  20. Multiple atoms encapsulated metallofullerenes Examples ; Er2@C82, La2@C78, La2@C80, La2@C84 Sc@C66,Sc3@C82, Sc3N@C82, Sc2@C82(Sc2@C84), Sc2C2@C84 Ti2C2@C78(Ti2@C80), Ti2@C82, Ti2C2@C82 Y2@C82, Y2C2@C82 etc. etc…. Issues Any special difference from M@C82 ? Entrapped atoms play differently or not?

  21. Multiple atoms in C82 cage Restricted to Y2C2@C82 (three isomers), Y2@C82(III), Lu2C2@C82, Ti2C2@C82 Reference : Sc2C2@C82 (Sc2@C84)

  22. Cage structure of three isomers : (I) Cs(6), (II) C2v(9), (III) C3v(8?) Different electronic structure, particularly in upper valence band region T. Inoue et al.

  23. C82 cage also contains metal atoms without carbon atoms. Y2C2@C82 and Y2@C82 give analogous absorption and have the same C3v cage structure Do they have analogous electronic structure ?

  24. The UPS of the two metallofullerenes are quite analogous ! The effect of two carbon atoms?

  25. Comparison of Y2@C82 and Y2C2@C82 (III)the same cage structure and entrapped metal atomsdifference is additional two carbon atoms. Cage symmetry seems to dominate the electronic structure ! Difference spectrum indicates additional two electron transfer in Y2@C82 (YC)24+@C824- and Y3+2@C826- Because Y3+ is the oxidation states of both fullerenes, carbon atoms accept two electrons or bonds is formed in (Y2C)2@C82

  26. No.2 Cs(b) No.3 C2(a) No.1 C2(b) No.4 Cs(c) No.5 C2(c) No.6 Cs(a) No.7 C3v No.9 C2v No.8 C3v This one !

  27. Conclusion obtained from Y atoms encapsulated fullerenes Additional two electrons might be use to form bonds between entrapped atoms or entrapped atoms and the cage What happens if you change the metal atoms inside the cage First example is Lu2C2@C82, then Ti2C2@C82

  28. when different species entrappedLu3+ and Y3+ The same C2v cages Lu2C2@C82 and Y2C2@C82(II) give the virtually identical spectra. Cage structure dominates ! BUT…

  29. C3v cages The UPS of the same C3v (8) cages Ti2C2@C82 and Y2C2@C82 are not identical ! Oxidation state of Ti in Ti2C2@C82 is +2, Y in Y2C2@C82 is +3 ! Oxidation state of entrapped atoms seems to be the key ! Electronic structure change might be introduced by strong interaction between the cage and entrapped species.

  30. Additional comment on Sc2@C84 But the UPS of Sc2@C84 and (YC)2@C82 resemble so well. NMR can be interpreted as C3v-(ScC)2@C82 C3v-(ScC)2@C82 is more reasonable ! It was said that Sc2@C84 has D2d symmetry.

  31. Summary of Mn@C82 • The electronic structure depends on • Cage structure (s-electron region) • Oxidation state of entrapped atom (upper valence p-band region) • Possibility of strong interaction between metal atoms and the cage • Oxidation states of metal may be the key • UPS is helpful to estimate the cage structure

  32. multiple atoms in C78 cage Restricted to (TiC)2@C78 (used to be Ti2@C80), La2@C78

  33. When it was synthesized, (TiC)2@C78 was thought to be Ti2@C80. The UPS was fairly well reproduced by calculation assuming Ti2@C80. But there are objection on the structure ! D3h – (TiC)2@C78 ?

  34. La2@C78 was also synthesized D3h symmetry

  35. No.1-D3 No.2-D2v No.3-D2v No.4-D3h No.5-D3h IPR satisfying C78 cages One of the important Issues There are two D3h structures. Are the structure of (TiC)2@C78 and La@C78 the same or not ?

  36. The UPS are quite different ! Indication of different cage?

  37. LDA-DFT calculation on two D3h cage structures with encapsulated La2 and (TiC)2 Good agreement on D3h (5) cage structure Although they have the same cage structure, but have the different electronic structures Oxidation states of entrapped atoms may be the key !

  38. Summary of Mn@C78 • Principally the cage dominate the electronic structure. • Entrapped atoms change upper valence drastically. Particularly the electronic structure of C78 cage is affected by entrapped species. • Small cage size affects arrangement of entrapped atoms more severely.

  39. An indication of structure of (MC)2 in metallofullerenes Approach from calculation Approach from XRD Ti2C2@C78 La2@C78 Inner space is so limited to accommodate multiple atoms. Small distance between the entrapped atoms and the cage affects the electronic structure of the cage.

  40. Summary (as for the effect of entrapped atoms to the electronic structure of the cage) • Mono metal atom encapsulated fullerenes • Cage dominate the electronic structure • Entrapped species have few influence • weak interaction between the cage and entrapped atom • Multiple atoms encapsulated fullerenes • Fullerenes with metals of the same oxidation state and the same cage give analogous electronic structure • Upper p-valence band depends on different oxidation states of entrapped species • Strong interaction is expected thanks to narrow inner space of fullerenes

  41. Experiments have been done here. UVSOR, IMS, Okazaki, Japan.

  42. Acknowledgements Measurements Chiba university Dr. K. Iwasaki, Mr. N. Wanita, Mr. M. Kato, Mr. T. Miyazaki, Mr. K. Furukawa Institute for Molecular Science (UVSOR) Dr. D. Yoshimura Sample preparation Tokyo Metropolitan University Prof. K. Kikuchi, Prof. Y. Achiba, Dr. T. Kodama Nagoya University Prof. H. Shinohara Fund A Grant-in-Aid for Scientific Research on Priority Area of Molecular Conductors (No. 15073203) from MEXT of Japan.

  43. Thank you for your attention

  44. Summary of Multiple atoms encapsulated fullerenes • Cage dominates s-electron levels. • p-levels are sensitive to entrapped atom species

  45. Photoelectron spectroscopy of fullerenes Spectral intensity change upon incident photon energy change Due to superposition of photoelectrons ejected from cage shaped molecules

  46. These metallofullerenes except Pr@C82 have the same C2v structure. Spectral shapes differ. Reason? Metal species or cage ?

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