Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Planar pentacoordinate carbons

Nature Reviews Chemistry volume 2, Article number: 0114 (2018) Cite this article

Subjects

Abstract

Carbon centres in typical organic molecules have a coordination number that can reach a maximum of four, in which case the bonded atoms are situated at the vertices of a tetrahedron. Exceptions to those two structural rules have been posited and examined for decades, and planar tetracoordinate carbon (ptC) species are notable molecules that violate the second rule. There is continued interest in experimental and theoretical studies of ptCs, as well as emerging molecules that contain planar pentacoordinate carbon (ppC) and planar hexacoordinate carbon (phC) atoms, species that violate both structural rules. This Review describes recent progress in the theoretical prediction of viable entities that contain ppC centres. The first such molecule reported, the D5h-symmetric ppC species CAl5+, was followed by a series of predicted ppC species that could be obtained by substituting the Al centres for other heteroatoms. More complicated ppC systems have also been suggested, including metallocene-stabilized ppCs and quasi-ppCs embedded within cage structures or 2D materials. To date, computational studies have identified at least 65 local and 39 global minimum energy structures that contain ppCs or quasi-ppCs. The general design principles for ptC-centred candidate structures include delocalization of the central C 2pz lone electron pair, ensuring an 18 valence electron count and allowing for strong electron delocalization. These principles have been extended to ppC systems with some success. It is hard to predict the extent to which the coordination number of planar C can be increased because it depends not only on the valence and size of C but also on the size of the atoms bonded to it and the mode of bonding. Although a few energetically low-lying planar hexacoordinate and heptacoordinate C species have been identified computationally, none have been observed experimentally.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Figure 1: The structures of two prominent planar tetracoordinate carbon-containing molecules.
Figure 2: Charge-neutral compounds featuring planar pentacoordinate or pseudopentacoordinate C bound to Li or B.
Figure 3: Structures featuring one or more planar pentacoordinate carbon centres surrounded by metal or metalloid atoms.
Figure 4: Many local minimum boron–carbon systems featuring one or two planar pentacoordinate carbons can be designed.
Figure 5: Monomeric and dimeric hexanuclear motifs are useful arrangements to stabilize planar pentacoordinate carbons.
Figure 6: Hexanuclear and heptanuclear planar pentacoordinate carbon anions have been found to be global minima.
Figure 7: Binding metal or halogen cations to the periphery of a planar pentacoordinate carbon can afford stable global minimum energy structures.
Figure 8: Predicted structures of planar pentacoordinate carbon-containing fullerenes, 2D materials and metallocenes.

References

  1. Tal’roze, V. L. & Ljubimova, A. K. Secondary processes in the ion source of a mass spectrometer. J. Mass Spectrom. 33, 502–504 (1998).

    Article  Google Scholar 

  2. Bartlett, P. D. Nonclassical Ions (WA Benjamin, New York, 1965).

    Google Scholar 

  3. Brown, H. C. The Nonclassical-Ion Problem (Plenum, New York, 1977).

    Book  Google Scholar 

  4. Olah, G. A., Prakash, G. K. S. & Saunders, M. Conclusion of the classical–nonclassical ion controversy based on the structural study of the 2-norbornyl cation. Acc. Chem. Res. 16, 440–448 (1983).

    Article  CAS  Google Scholar 

  5. Minkin, V. I., Minyaev, R. M. & Hoffmann, R. Nonclassical structures of organic compounds: non-standard stereochemistry and hypercoordination. Russ. Chem. Rev. 71, 869–892 (2002).

    Article  CAS  Google Scholar 

  6. Olah, G. A. My search for carbocations and their role in chemistry (Nobel lecture). Angew. Chem. Int. Ed. 34, 1393–1405 (1995).

    Article  CAS  Google Scholar 

  7. Monkhorst, H. J. Activation energy for interconversion of enantiomers containing an asymmetric carbon atom without breaking bonds. Chem. Commun. 1111–1112 (1968).

  8. Hoffmann, R., Alder, R. W. & Wilcox, C. F. Planar tetracoordinate carbon. J. Am. Chem. Soc. 92, 4992–4993 (1970).

    Article  CAS  Google Scholar 

  9. Pepper, M. J. M. et al. Is the stereomutation of methane possible? J. Comput. Chem. 16, 207–225 (1995).

    Article  CAS  Google Scholar 

  10. Gordon, M. S. & Schmidt, M. W. Does methane invert through square planar? J. Am. Chem. Soc. 115, 7486–7492 (1993).

    Article  CAS  Google Scholar 

  11. Sorger, K. & Schleyer, P. v. R. Planar and inherently non-tetrahedral tetracoordinate carbon: a status report. J. Mol. Struct. 338, 317–346 (1995).

    Article  Google Scholar 

  12. Keese, R. Carbon flatland: planar tetracoordinate carbon and fenestranes. Chem. Rev. 106, 4787–4808 (2006).

    Article  CAS  Google Scholar 

  13. Collins, J. B. et al. Stabilization of planar tetracoordinate carbon. J. Am. Chem. Soc. 98, 5419–5427 (1976).

    Article  CAS  Google Scholar 

  14. Cotton, F. A. & Millar, M. The probable existence of a triple bond between two vanadium atoms. J. Am. Chem. Soc. 99, 7886–7891 (1977).

    Article  CAS  Google Scholar 

  15. Schleyer, P. v. R. & Boldyrev, A. I. A new, general strategy for achieving planar tetracoordinate geometries for carbon and other second row periodic elements. J. Chem. Soc., Chem. Commun. 1536–1538 (1991).

  16. Boldyrev, A. I. & Simons, J. Tetracoordinated planar carbon in pentaatomic molecules. J. Am. Chem. Soc. 120, 7967–7972 (1998).

    Article  CAS  Google Scholar 

  17. Cui, Z.-H., Shao, C.-B., Gao, S.-M. & Ding, Y.-H. Pentaatomic planar tetracoordinate carbon molecules [XCAl3]q [(X. q) = (B, −2), (C, −1), (N, 0)] with C–X multiple bonding. Phys. Chem. Chem. Phys. 12, 13637–13645 (2010).

    Article  CAS  Google Scholar 

  18. Castro, A. C. et al. Planar tetracoordinate carbon in CE42− (E = Al–Ti) clusters. Chem. Phys. Lett. 519–520, 29–33 (2012).

    Article  Google Scholar 

  19. Cui, Z.-H. et al. Planar tetracoordinate carbons with a double bond in CAl3E clusters. Phys. Chem. Chem. Phys. 17, 8769–8775 (2015).

    Article  CAS  Google Scholar 

  20. Li, X., Wang, L.-S., Boldyrev, A. I. & Simons, J. Tetracoordinated planar carbon in the Al4C− anion. A combined photoelectron spectroscopy and ab initio study. J. Am. Chem. Soc. 121, 6033–6038 (1999).

    Article  CAS  Google Scholar 

  21. Wang, L.-S., Boldyrev, A. I., Li, X. & Simons, J. Experimental observation of pentaatomic tetracoordinate planar carbon-containing molecules. J. Am. Chem. Soc. 122, 7681–7687 (2000).

    Article  CAS  Google Scholar 

  22. Albrecht, M., Erker, G. & Kruger, C. The synthesis of stable, isolable planar-tetracoordinate carbon compounds. Synlett 441–448 (1993).

  23. Evans, W. J., Keyer, R. A. & Ziller, J. W. Investigation of organolanthanide-based carbon–carbon bond formation: synthesis, structure, and coupling reactivity of organolanthanide alkynide complexes, including the unusual structures of the trienediyl complex [(C5Me5)2Sm]2[μ-η2:η2-Ph(CH2)2C=C=C=C-(CH2)2Ph] and the unsolvated alkynide [(C5Me5)2Sm(C≡CCMe3)]2 . Organometallics 12, 2618–2633 (1993).

    Article  CAS  Google Scholar 

  24. Rö ttger, D. & Erker, G. Compounds containing planar-tetracoordinate carbon. Angew. Chem. Int. Ed. 36, 812–827 (1997).

    Article  Google Scholar 

  25. Choukroun, R. & Cassoux, P. Planar tetracoordination of carbon in groups 4 and 5 organometallic chemistry. Acc. Chem. Res. 32, 494–502 (1999).

    Article  CAS  Google Scholar 

  26. Choukroun, R. & Lorber, C. Adventures in vanadocene chemistry. Eur. J. Inorg. Chem. 4683–4692 (2005).

  27. Su, M.-D. Theoretical designs for planar tetracoordinated carbon in Cu, Ag, and Au organometallic chemistry: a new target for synthesis. Inorg. Chem. 44, 4829–4833 (2005).

    Article  CAS  Google Scholar 

  28. Suresh, C. H. & Frenking, G. Direct 1–3 metal–carbon bonding and planar tetracoordinated carbon in group 6 metallacyclobutadienes. Organometallics 29, 4766–4769 (2010).

    Article  CAS  Google Scholar 

  29. Jia, X. F. & Zhang, C. J. Structure, bonding and reactivity of coinage metal complexes TML2 and TML2+ (TM = Cu, Ag, Au) with planar tetracoordinate carbon, a theoretical investigation. Comput. Theor. Chem. 1075, 47–53 (2016).

    Article  CAS  Google Scholar 

  30. Merino, G., Mendez-Rojas, M. A. & Vela, A. (C5M2−n)n− (M = Li, Na, K, and n = 0, 1, 2). A new family of molecules containing planar tetracoordinate carbons. J. Am. Chem. Soc. 125, 6026–6027 (2003).

    Article  CAS  Google Scholar 

  31. Pérez-Peralta, N. et al. Stabilizing carbon–lithium stars. Phys. Chem. Chem. Phys. 13, 12975–12980 (2011).

    Article  Google Scholar 

  32. Perez, N. et al. Planar tetracoordinate carbons in cyclic hydrocarbons. Org. Lett. 7, 1509–1512 (2005).

    Article  CAS  Google Scholar 

  33. Merino, G., Méndez-Rojas, M. A., Vela, A. & Heine, T. Recent advances in planar tetracoordinate carbon chemistry. J. Comput. Chem. 28, 362–372 (2007).

    Article  CAS  Google Scholar 

  34. Perez-Peralta, N. et al. Planar tetracoordinate carbons in cyclic semisaturated hydrocarbons. J. Org. Chem. 73, 7037–7044 (2008).

    Article  CAS  Google Scholar 

  35. Cui, Z.-H., Contreras, M., Ding, Y.-H. & Merino, G. Planar tetracoordinate carbon versus planar tetracoordinate boron: the case of CB4 and its cation. J. Am. Chem. Soc. 133, 13228–13231 (2011).

    Article  CAS  Google Scholar 

  36. Wu, Y.-B. et al. Starlike aluminum–carbon aromatic species. Chem. Eur. J. 17, 714–719 (2011).

    Article  CAS  Google Scholar 

  37. Crigger, C., Wittmaack, B. K., Tawfik, M., Merino, G. & Donald, K. J. Plane and simple: planar tetracoordinate carbon centers in small molecules. Phys. Chem. Chem. Phys. 14, 14775–14783 (2012).

    Article  CAS  Google Scholar 

  38. Pan, S. et al. C5Li7+ and O2Li5+ as noble-gas-trapping agents. Chem. Eur. J. 19, 2322–2329 (2013).

    Article  CAS  Google Scholar 

  39. Bomble, L., Steinmann, S., Perez-Peralta, N., Merino, G. & Corminboeuf, C. Bonding analysis of planar hypercoordinate atoms via the generalized BLW-LOL analysis. J. Comput. Chem. 34, 2242–2248 (2013).

    Article  CAS  Google Scholar 

  40. Bolton, E. E., Laidig, W. D., Schleyer, P. v. R. & Schaefer, H. F. Does singlet 1,1-dilithioethene really prefer a perpendicular structure? J. Phys. Chem. 99, 17551–17557 (1995).

    Article  CAS  Google Scholar 

  41. Wang, Z.-X. & Schleyer, P. v. R. Construction principles of “hyparenes”: families of molecules with planar pentacoordinate carbons. Science 292, 2465–2469 (2001).

    Article  CAS  Google Scholar 

  42. Wang, Z.-X. & Schleyer, P. v. R. Planar hypercoordinate carbons joined: wheel-shaped molecules with C–C axles. Angew. Chem. Int. Ed. 41, 4082–4085 (2002).

    Article  CAS  Google Scholar 

  43. Li, S.-D., Miao, C.-Q. & Ren, G.-M. D5 Cu5H5X: pentagonal hydrocopper Cu5H5 containing pentacoordinate planar nonmetal centers (X = B, C, N, O). Eur. J. Inorg. Chem. 2232–2234 (2004).

  44. Li, S.-D., Guo, Q.-L., Miao, C.-Q. & Ren, G.-M. Investigation on transition-metal hydrometal complexes MnHnC with planar coordinate carbon centers by density functional theory. Acta Phys. Chim. Sin. 23, 743–745 (2007).

    Google Scholar 

  45. Erhardt, S., Frenking, G. & Chen, Z. F. & Schleyer, P. v. R. Aromatic boron wheels with more than one carbon atom in the center: C2B8, C3B93+, and C5B11+. Angew. Chem. Int. Ed. 44, 1078–1082 (2005).

    Article  CAS  Google Scholar 

  46. Luo, Q. Theoretical observation of hexaatomic molecules containing pentacoordinate planar carbon. Sci. China Ser. B Chem. 51, 1030–1035 (2008).

    Article  CAS  Google Scholar 

  47. Pei, Y., An, W., Ito, K., Schleyer, P. v. R. & Zeng, X. C. Planar pentacoordinate carbon in CAl5+: a global minimum. J. Am. Chem. Soc. 130, 10394–10400 (2008).

    Article  CAS  Google Scholar 

  48. Pei, Y. & Zeng, X. C. Probing the planar tetra-, penta-, and hexacoordinate carbon in carbon–boron mixed clusters. J. Am. Chem. Soc. 130, 2580–2592 (2008).

    Article  CAS  Google Scholar 

  49. Averkiev, B. B. et al. Carbon avoids hypercoordination in CB6−, CB62−, and C2B5− planar carbon–boron clusters. J. Am. Chem. Soc. 130, 9248–9250 (2008).

    Article  CAS  Google Scholar 

  50. Liang, J.-X., Jia, W.-H., Zhang, C.-J. & Cao, Z.-X. Unusual boron–carbon compounds containing planar tetracoordinate and pentacoordinate carbons. Acta Phys. Chim. Sin. 25, 1847–1852 (2009).

    CAS  Google Scholar 

  51. Zdetsis, A. D. Success and pitfalls of the Sin − 2C2H2–C2Bn−2Hn isolobal analogy: depth and breadth of the boron connection. J. Chem. Phys. 130, 064303 (2009).

    Article  Google Scholar 

  52. Zdetsis, A. D. Novel pentagonal silicon rings and nanowheels stabilized by flat pentacoordinate carbon(s). J. Chem. Phys. 134, 094312 (2011).

    Article  Google Scholar 

  53. Yamaguchi, W. δ and σ versus π conflicting aromatic pentagonal ring of tungsten with a planar pentacoordinate carbon at the ring center. Int. J. Quantum Chem. 110, 1086–1091 (2010).

    Article  CAS  Google Scholar 

  54. Merino, G. & Solà, M. Celebrating the 150th anniversary of the Kekulé benzene structure. Phys. Chem. Chem. Phys. 18, 11587–11588 (2016).

    Article  Google Scholar 

  55. Hoffmann, R. The many guises of aromaticity. Am. Sci. 103, 18 (2015).

    Article  Google Scholar 

  56. Li, X., Kuznetsov, A. E., Zhang, H.-F., Boldyrev, A. I. & Wang, L.-S. Observation of all-metal aromatic molecules. Science 291, 859–861 (2001).

    Article  CAS  Google Scholar 

  57. Kuznetsov, A. E. et al. All-metal antiaromatic molecule: rectangular Al44− in the Li3Al4− anion. Science 300, 622–625 (2003).

    Article  CAS  Google Scholar 

  58. Islas, R., Heine, T. & Merino, G. Structure and electron delocalization in Al42− and Al44−. J. Chem. Theory Comput. 3, 775–781 (2007).

    Article  CAS  Google Scholar 

  59. Jimenez-Halla, J. O. C. et al. CAl4Be and CAl3Be2−: global minima with a planar pentacoordinate carbon atom. Chem. Commun. 46, 8776–8778 (2010).

    Article  CAS  Google Scholar 

  60. Castro, A. C. et al. CBe5E− (E = Al, Ga, In, Tl): planar pentacoordinate carbon in heptaatomic clusters. Phys. Chem. Chem. Phys. 14, 14764–14768 (2012).

    Article  CAS  Google Scholar 

  61. Wu, Y.-B., Duan, Y., Lu, H.-G. & Li, S.-D. CAl2Be32− and its salt complex LiCAl2Be3−: anionic global minima with planar pentacoordinate carbon. J. Phys. Chem. A 116, 3290–3294 (2012).

    Article  CAS  Google Scholar 

  62. Zhang, X.-Y. & Ding, Y.-H. CAl4Ga+. Comput. Theor. Chem. 1048, 18–24 (2014).

    Article  CAS  Google Scholar 

  63. Grande-Aztatzi, R. et al. Planar pentacoordinate carbons in CBe54− derivatives. Phys. Chem. Chem. Phys. 17, 4620–4624 (2015).

    Article  CAS  Google Scholar 

  64. Guo, J.-C. et al. CBe5Hnn−4 (n = 2–5): hydrogen-stabilized CBe5 pentagons containing planar or quasi-planar pentacoordinate carbons. J. Phys. Chem. A 119, 13101–13106 (2015).

    Article  CAS  Google Scholar 

  65. Guo, J.-C. et al. Star-like superalkali cations featuring planar pentacoordinate carbon. J. Chem. Phys. 144, 244303 (2016).

    Article  Google Scholar 

  66. Cui, Z.-H., Sui, J.-J. & Ding, Y.-H. How can carbon favor planar multi-coordination in boron-based clusters? Global structures of CBxEy2− (E = Al, Ga. x + y = 4). Phys. Chem. Chem. Phys. 17, 32016–32022 (2015).

    Article  CAS  Google Scholar 

  67. Hou, J. H. et al. Exploring the geometrical structures of X©BnHnm [(X. m) = (B, +1), (C, +2) for n = 5; (X, m) = (Be, 0), (B, +1) for n = 6] by an electronic method. New J. Chem. 39, 8630–8637 (2015).

    Article  CAS  Google Scholar 

  68. Gribanova, T. N., Minyaev, R. M. & Minkin, V. I. Structure and stability of the C-doped boron fullerenes B60C12 and B80C12 with quasi-planar pentacoordinated cage carbon atoms: a quantum-chemical study. Mendeleev Commun. 26, 485–487 (2016).

    Article  CAS  Google Scholar 

  69. Wang, Y., Li, F., Li, Y. F. & Chen, Z. F. Semi-metallic Be5C2 monolayer global minimum with quasi-planar pentacoordinate carbons and negative Poisson's ratio. Nat. Commun. 7, 11488 (2016).

    Article  CAS  Google Scholar 

  70. Li, J.-J. et al. Zigzag double-chain C–Be nanoribbon featuring planar pentacoordinate carbons and ribbon aromaticity. J. Mater. Chem. C 5, 408–414 (2017).

    Article  CAS  Google Scholar 

  71. Cui, Z.-H. et al. Planar pentacoordinate carbon atoms embedded in a metallocene framework. Chem. Commun. 53, 138–141 (2017).

    Article  CAS  Google Scholar 

  72. Exner, K. & Schleyer, P. v. R. Planar hexacoordinate carbon: a viable possibility. Science 290, 1937–1940 (2000).

    Article  CAS  Google Scholar 

  73. Islas, R., Heine, T., Ito, K., Schleyer, P. v. R. & Merino, G. Boron rings enclosing planar hypercoordinate group 14 elements. J. Am. Chem. Soc. 129, 14767–14774 (2007).

    Article  CAS  Google Scholar 

  74. Wang, L.-M., Huang, W., Averkiev, B. B., Boldyrev, A. I. & Wang, L.-S. CB7−: experimental and theoretical evidence against hypercoordinate planar carbon. Angew. Chem. Int. Ed. 46, 4550–4553 (2007).

    Article  CAS  Google Scholar 

  75. Wu, Y.-B. et al. D3h CN3Be3+ and CO3Li3+: viable planar hexacoordinate carbon prototypes. Phys. Chem. Chem. Phys. 14, 14760–14763 (2012).

    Article  CAS  Google Scholar 

  76. Zhang, C.-F., Han, S.-J., Wu, Y.-B., Lu, H.-G. & Lu, G. Thermodynamic stability versus kinetic stability: is the planar hexacoordiante carbon species D3h CN3Mg3+ viable? J. Phys. Chem. A 118, 3319–3325 (2014).

    Article  CAS  Google Scholar 

  77. Li, Y., Liao, Y. & Chen, Z. Be2C monolayer with quasi-planar hexacoordinate carbons: a global minimum structure. Angew. Chem. Int. Ed. 53, 7248–7252 (2014).

    Article  CAS  Google Scholar 

  78. Heine, T. & Merino, G. What is the maximum coordination number in a planar structure? Angew. Chem. Int. Ed. 51, 4275–4276 (2012).

    Article  CAS  Google Scholar 

  79. Zhao, T., Wang, Q. & Jena, P. Cluster-inspired design of high-capacity anode for Li-ion batteries. ACS Energy Lett. 1, 202–208 (2016).

    Article  CAS  Google Scholar 

  80. Dai, J., Wu, X., Yang, J. & Zeng, X. C. AlxC monolayer sheets: two-dimensional networks with planar tetracoordinate carbon and potential applications as donor material in solar cell. J. Phys. Chem. Lett. 5, 2058–2065 (2014).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

The authors acknowledge the generous support from Conacyt (Grand CB-2015-252356). V.V.-G. thanks Conacyt for the awarding of a fellowship. K.J.D. was supported in Richmond by the National Science Foundation (NSF-CAREER Award CHE-1056430 and the Henry Dreyfus Teacher-Scholar Awards Program. S.P. thanks Nanjing Tech University for his postdoctoral fellowship.

Author information

Authors and Affiliations

  1. Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados, Mérida, México

    Valentin Vassilev-Galindo & Gabriel Merino

  2. Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing, China

    Sudip Pan

  3. Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, VA, USA

    Kelling J. Donald

Authors
  1. Valentin Vassilev-Galindo
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Sudip Pan
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kelling J. Donald
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Gabriel Merino
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

All authors contributed equally to the preparation of this manuscript.

Corresponding author

Correspondence to Gabriel Merino.

Ethics declarations

Competing interests

The authors declare no competing interests.

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Vassilev-Galindo, V., Pan, S., Donald, K. et al. Planar pentacoordinate carbons. Nat Rev Chem 2, 0114 (2018). https://doi.org/10.1038/s41570-018-0114

Download citation

  • Published:

  • DOI: https://doi.org/10.1038/s41570-018-0114

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing