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Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids


Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely after reports of superconductivity in a number of potassium- and rubidium-intercalated materials. There are, however, no reported crystal structures to inform our understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K2Pentacene and K2Picene by a solid–solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, and so enables the determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, in which the cation sites are pre-defined by the host structure.

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Figure 1: Available void space in carbon-based molecular crystal structures.
Figure 2: Characterization data for K2Pentacene.
Figure 3: Crystal structure of K2Pentacene.
Figure 4: Characterization data for K2Picene.
Figure 5: Crystal structure of K2Picene.
Figure 6: Local structure in K2Picene.


  1. 1

    Fleming, R. M. et al. Relation of structure and superconducting transition temperatures in A3C60 . Nature 352, 787–788 (1991).

    CAS  Article  Google Scholar 

  2. 2

    Hebard, A. F. et al. Superconductivity at 18 K in potassium doped C60 . Nature 350, 600–601 (1991).

    CAS  Article  Google Scholar 

  3. 3

    Tanigaki, K. et al. Superconductivity at 33 K in CsxRbyC60 . Nature 352, 222–223 (1991).

    CAS  Article  Google Scholar 

  4. 4

    Ekimov, E. A. et al. Superconductivity in diamond. Nature 428, 542–545 (2004).

    CAS  Article  Google Scholar 

  5. 5

    Weller, T. E., Ellerby, M., Saxena, S. S., Smith, R. P. & Skipper, N. T. Superconductivity in the intercalated graphite compounds C6Yb and C6Ca. Nat. Phys. 1, 39–41 (2005).

    CAS  Article  Google Scholar 

  6. 6

    Ganin, A. Y. et al. Bulk superconductivity at 38 K in a molecular system. Nat. Mater. 7, 367–371 (2008).

    CAS  Article  Google Scholar 

  7. 7

    Stephens, P. W. et al. Structure of single phase superconducting K3C60 . Nature 351, 632–634 (1991).

    CAS  Article  Google Scholar 

  8. 8

    Mitsuhashi, R. et al. Superconductivity in alkali-metal-doped picene. Nature 464, 76–79 (2010).

    CAS  Article  Google Scholar 

  9. 9

    Wang, X. F. et al. Superconductivity at 5 K in alkali-metal-doped phenanthrene. Nat. Commun. 2, 507 (2011).

    CAS  Article  Google Scholar 

  10. 10

    Kubozono, Y. et al. Metal-intercalated aromatic hydrocarbons: a new class of carbon-based superconductors. Phys. Chem. Chem. Phys. 13, 16476–16493 (2011).

    CAS  Article  Google Scholar 

  11. 11

    Xue, M. et al. Superconductivity above 30 K in alkali-metal-doped hydrocarbon. Sci. Rep. 2, 389 (2012).

    Article  Google Scholar 

  12. 12

    Trotter, J. Crystal and molecular structure of phenanthrene. Acta Crystallogr. 16, 605–608 (1963).

    CAS  Article  Google Scholar 

  13. 13

    De, A., Ghosh, R., Roychowdhury, S. & Roychowdhury, P. Structural analysis of picene, C22H14 . Acta Crystallogr. C 41, 907–909 (1985).

    Article  Google Scholar 

  14. 14

    Kaefer, D., El Helou, M., Gemel, C. & Witte, G. Packing of planar organic molecules: interplay of van der Waals and electrostatic interaction. Cryst. Growth Des. 8, 3053–3057 (2008).

    Article  Google Scholar 

  15. 15

    Burgi, H. B., Restori, R. & Schwarzenbach, D. Structure of C60—partial orientational order in the room-temperature modification of C60 . Acta Crystallogr. B 49, 832–838 (1993).

    Article  Google Scholar 

  16. 16

    Desiraju, G. R. & Gavezzotti, A. Crystal structures of polynuclear aromatic hydrocarbons—classification, rationalization and prediction from molecular structure. Acta Crystallogr. B 45, 473–482 (1989).

    Article  Google Scholar 

  17. 17

    Mori, T. & Ikehata, S. ESR study on potassium doped pentacene. Solid State Commun. 101, 213–218 (1997).

    CAS  Article  Google Scholar 

  18. 18

    Phan, Q. T. N., Heguri, S., Tanabe, Y., Shimotani, H. & Tanigaki, K. Systematic study of the electronic states in electron-doped polyacenes. Eur. J. Inorg. Chem. 4033– 4038 (2014).

    Google Scholar 

  19. 19

    Phan, Q. T. N. et al. Two different ground states in K-intercalated polyacenes. Phys. Rev. B 93, 075130 (2016).

    Article  Google Scholar 

  20. 20

    Nanditha, D. M. et al. Nanoimprinted large area heterojunction pentacene-C60 photovoltaic device. Appl. Phys. Lett. 90, 253502 (2007).

    Article  Google Scholar 

  21. 21

    Koch, N. Organic electronic devices and their functional interfaces. Chem. Phys. Chem. 8, 1438–1455 (2007).

    CAS  Article  Google Scholar 

  22. 22

    Yamashita, Y. Organic semiconductors for organic field-effect transistors. Sci. Technol. Adv. Mater. 10, 024313 (2009).

    Article  Google Scholar 

  23. 23

    Craciun, M. F. et al. Evidence for the formation of a Mott state in potassium-intercalated pentacene. Phys. Rev. B 79, 125116 (2009).

    Article  Google Scholar 

  24. 24

    Minakata, T., Ozaki, M. & Imai, H. Conducting thin films of pentacene doped with alkaline metals. J. Appl. Phys. 74, 1079–1082 (1993).

    CAS  Article  Google Scholar 

  25. 25

    Vanýsek, J. CRC Handbook of Chemistry and Physics (CRC, 2011).

    Google Scholar 

  26. 26

    Bergman, I. The polarography of polycyclic aromatic hydrocarbons and the relationship between their half-wave potentials and absorption spectra. Trans. Faraday Soc. 50, 829–838 (1954).

    CAS  Article  Google Scholar 

  27. 27

    Szczepanski, J., Wehlburg, C. & Vala, M. Vibrational and electronic spectra of matrix isolated pentacene cations and anions. Chem. Phys. Lett. 232, 221–228 (1995).

    CAS  Article  Google Scholar 

  28. 28

    Mattheus, C. C. et al. Polymorphism in pentacene. Acta Crystallogr. C 57, 939–941 (2001).

    CAS  Article  Google Scholar 

  29. 29

    Desiraju, G. R. & Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology (Oxford Science, 1999).

    Google Scholar 

  30. 30

    Scott, T. A. et al. After 118 years, the isolation of two common radical anion reductants as simple, stable solids. Chem. Commun. 65–67 (2009).

  31. 31

    Bock, H., Gharagozloo-Hubmann, K., Sievert, M., Prisner, T. & Havlas, Z. Single crystals of an ionic anthracene aggregate with a triplet ground state. Nature 404, 267–269 (2000).

    CAS  Article  Google Scholar 

  32. 32

    Takabayashi, Y. et al. π-electron S = 1/2 quantum spin-liquid state in an ionic polyaromatic hydrocarbon. Nat. Chem. (2017).

    Google Scholar 

  33. 33

    Kambe, T. et al. Synthesis and physical properties of metal-doped picene solids. Phys. Rev. B 86, 214507 (2012).

    Article  Google Scholar 

  34. 34

    Ferrari, A. C. & Robertson, J. Raman spectroscopy of amorphous, nanostructured, diamond-like carbon, and nanodiamond. Phil. Trans. R. Soc. Lond. A 362, 2477–2512 (2004).

    CAS  Article  Google Scholar 

  35. 35

    Naghavi, S. S. & Tosatti, E. Crystal structure search and electronic properties of alkali-doped phenanthrene and picene. Phys. Rev. B 90, 075143 (2014).

    Article  Google Scholar 

  36. 36

    Kamaras, K. & Klupp, G. Metallicity in fullerides. Dalton Trans. 43, 7366–7378 (2014).

    CAS  Article  Google Scholar 

  37. 37

    Claudia, A.-D., Dmitrii, N., Peter, P. & Christian, M. The role of polymorphism in organic thin films: oligoacenes investigated from first principles. New J. Phys. 11, 125010 (2009).

    Article  Google Scholar 

  38. 38

    Kosugi, T., Miyake, T., Ishibashi, S., Arita, R. & Aoki, H. First-principles electronic structure of solid picene. J. Phys. Soc. Jpn 78, 113704 (2009).

    Article  Google Scholar 

  39. 39

    Ruff, A. et al. Absence of metallicity in K-doped picene: importance of electronic correlations. Phys. Rev. Lett. 110, 216403 (2013).

    Article  Google Scholar 

  40. 40

    Werner, P. & Millis, A. J. High-spin to low-spin and orbital polarization transitions in multiorbital Mott systems. Phys. Rev. Lett. 99, 126405 (2007).

    Article  Google Scholar 

  41. 41

    Larson, A. C. & von Dreele, R. General Structure Analysis System (GSAS) (Los Alamos National Laboratory Report No. LAUR 86-748, 1994).

  42. 42

    Toby, B. H. EXPGUI, a graphical user interface for GSAS. J. Appl. Crystallogr. 34, 210–213 (2001).

    CAS  Article  Google Scholar 

  43. 43

    Coelho, A. A. TOPAS-Academic v5 (Coelo Software, 2012).

  44. 44

    Favre-Nicolin, V. & Cerny, R. FOX, ‘free objects for crystallography’: a modular approach to ab initio structure determination from powder diffraction. J. Appl. Crystallogr. 35, 734–743 (2002).

    CAS  Article  Google Scholar 

  45. 45

    Stokes, H. T. & Hatch, D. M. FINDSYM: program for identifying the space-group symmetry of a crystal. J. Appl. Crystallogr. 38, 237–238 (2005).

    CAS  Article  Google Scholar 

  46. 46

    Kresse, G. & Furthmuller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B. 54, 11169–11186 (1996).

    CAS  Article  Google Scholar 

  47. 47

    Klimes, J., Bowler, D. R. & Michaelides, A. Van der Waals density functionals applied to solids. Phys. Rev. B 83, 195131 (2011).

    Article  Google Scholar 

  48. 48

    Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

    CAS  Article  Google Scholar 

  49. 49

    Curtarolo, S. et al. AFLOW: an automatic framework for high-throughput materials discovery. Comput. Mater. Sci. 58, 218–226 (2012).

    CAS  Article  Google Scholar 

  50. 50

    Lorente, N. & Persson, M. Theoretical aspects of tunneling-current-induced bond excitation and breaking at surfaces. Faraday Discuss. 117, 277–290 (2000).

    CAS  Article  Google Scholar 

  51. 51

    Fleming, R. M. et al. Preparation and structure of the alkali-metal fulleride A4C60 . Nature 352, 701–703 (1991).

    CAS  Article  Google Scholar 

  52. 52

    Zhou, O. et al. Structure and bonding in alkali-metal-doped C60 . Nature 351, 462–464 (1991).

    CAS  Article  Google Scholar 

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We acknowledge financial support from the UK Engineering and Physical Sciences Research Council (EP/K027255 and EP/K027212), the European Union/JST SICORP-LEMSUPER FP7-NMP-2011-EU-Japan project (contract no. NMP3-SL-2011-283214), the Mitsubishi Foundation, the Japan Society for the Promotion of Science under the Scientific Research on Innovative Areas ‘J-Physics’ Project (no. 15H05882), the ‘World Premier International (WPI) Research Center Initiative for Atoms, Molecules and Materials,’ the Ministry of Education, Culture, Sports, Science, and Technology of Japan and the Japan Science and Technology Agency under the ERATO Isobe Degenerate π-Integration Project. We thank the Diamond Light Source for access to synchrotron X-ray facilities, and C. C. Tang, C. A. Murray and P. Adamson for beamline assistance. We thank Katalin Kamarás for help with the infrared measurements. We thank M. Persson for the use of his XVASP code and related external routines for projecting density of states onto molecular orbitals. We thank the Royal Society for a Newton International Fellowship (G.K.). M.J.R. is a Royal Society Research Professor.

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K.P. and M.J.R. conceived and designed the project. M.J.R. directed and coordinated the research. F.D.R. carried out the initial syntheses using KH that identified both phases, performed the initial structure determination of both phases and performed Raman measurements. M.J.P. completed the structural analyses with C.I.H. and C.C. C.I.H. performed the final syntheses and, with M.J.P., finalized the link between synthesis and structure. G.F.S.W. defined the structural evolution of the intermolecular interactions. S.K. and A.Y.G. developed early reaction protocols, and R.H.C. undertook early structural work. D.A. computed the evolution of the void space within the material that connects the molecular packing to the cation distribution. M.S.D. performed and interpreted electronic structure calculations. G.K. performed and interpreted Raman and infrared measurements. F.D.R. and M.J.R. wrote the first draft of the paper, which was then completed with input from all the authors.

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Correspondence to K. Prassides or M. J. Rosseinsky.

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The authors declare no competing financial interests.

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Romero, F., Pitcher, M., Hiley, C. et al. Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids. Nature Chem 9, 644–652 (2017).

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