Chemistry:Triangulene

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Triangulene
Triangulene
Names
Preferred IUPAC name
Dibenzo[cd,mn]pyrene-4,8-diyl
Other names
[3]Triangulene
Identifiers
3D model (JSmol)
ChemSpider
Properties
C22H12
Molar mass 276.338 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
Tracking categories (test):

Triangulene (also known as Clar's hydrocarbon) is the smallest triplet-ground-state polybenzenoid.[1] It exists as a biradical with the chemical formula C22H12.[2] It was first hypothesized by Czech chemist Erich Clar in 1953.[3] Its first confirmed synthesis was published in a February 2017 issue of Nature Nanotechnology, in a project led by researchers David Fox and Anish Mistry at the University of Warwick in collaboration with IBM.[4] Other attempts by Japan ese researchers have been successful only in making substituted triangulene derivatives.[5]

A six-step synthesis yielded two isomers of dihydrotriangulene which were then deposited on xenon or copper base. The researchers used a combined scanning tunneling and atomic force microscope (STM/AFM) to remove individual hydrogen atoms. The synthesized molecule of triangulene remained stable at high-vacuum low-temperature conditions for four days, giving the scientists plenty of time to characterize it (also using STM/AFM).[4]

[n]Triangulenes

Triangulene, as defined here, is a member of a wider class of [n]triangulenes, where n is the number of hexagons along an edge of the molecule. Thus, triangulene may also be referred to as [3]triangulene.

Theory

A tight-binding description of the molecular orbitals of [n]triangulenes predicts[6] that [n]triangulenes have (n − 1) unpaired electrons, which are associated to (n − 1) non-bonding states. When electron–electron interactions are included, theory predicts[6][7][8] that the ground state total spin quantum number S of [n]triangulenes is S = n − 1/2. Thus, [3]triangulenes are predicted to have an S = 1 ground state. The intramolecular exchange interaction in triangulene, which determines the energy difference between the S = 1 ground state and the S = 0 excited state, is predicted to be the largest[9] among all polycyclic aromatic hydrocarbon (PAH) diradicals, due to maximum overlap of the wave function of the unpaired electrons.

The ground state spin of [n]triangulenes can be rationalized[6] in terms of a theorem[10] by Elliot H. Lieb, which relates, for a bipartite lattice, the ground state spin of the Hubbard model at half filling to the sublattice imbalance.

Experiments

So far, the ultra-high vacuum on-surface syntheses of [n]triangulenes with n = 3,[4] 4,[11] 5[12] and 7[13] (the hitherto largest triangulene homologue) have been reported. In addition, the on-surface synthesis of [3]triangulene dimers[14] has also been reported, where inelastic electron tunneling spectroscopy provides a direct evidence of a strong antiferromagnetic coupling between the triangulenes. In 2021, an international team of researchers reported the fabrication of [3]triangulene-based quantum spin chains on a gold surface,[15] where signatures of both spin fractionalization and Haldane gap were observed.

References

  1. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "biradical". doi:10.1351/goldbook.B00671
  2. ↑ "triangulene | C22H12 | ChemSpider". http://www.chemspider.com/Chemical-Structure.58825768.html. 
  3. ↑ Ball, Philip (February 2017). "Elusive triangulene created by moving atoms one at a time". Nature 542 (7641): 284–285. doi:10.1038/nature.2017.21462. PMID 28202993. Bibcode: 2017Natur.542..284B. 
  4. ↑ 4.0 4.1 4.2 Pavliček, Niko; Mistry, Anish; Majzik, Zsolt; Moll, Nikolaj; Meyer, Gerhard; Fox, David J.; Gross, Leo (April 2017). "Synthesis and characterization of triangulene". Nature Nanotechnology 12 (4): 308–311. doi:10.1038/nnano.2016.305. PMID 28192389. Bibcode: 2017NatNa..12..308P. http://wrap.warwick.ac.uk/86722/1/WRAP_ch-030317-wrap_-cusersdavid_foxdesktop40triangulene_complete_accepted.pdf. 
  5. ↑ Morita, Yasushi; Suzuki, Shuichi; Sato, Kazunobu; Takui, Takeji (2011). "Synthetic organic spin chemistry for structurally well-defined open-shell graphene fragments". Nature Chemistry 3 (3): 197–204. doi:10.1038/nchem.985. PMID 21336324. Bibcode: 2011NatCh...3..197M. 
  6. ↑ 6.0 6.1 6.2 Fernández-Rossier, J.; Palacios, J. J. (23 October 2007). "Magnetism in Graphene Nanoislands". Physical Review Letters 99 (17): 177204. doi:10.1103/PhysRevLett.99.177204. PMID 17995364. Bibcode: 2007PhRvL..99q7204F. 
  7. ↑ Wang, Wei L.; Meng, Sheng; Kaxiras, Efthimios (1 January 2008). "Graphene NanoFlakes with Large Spin". Nano Letters 8 (1): 241–245. doi:10.1021/nl072548a. PMID 18052302. Bibcode: 2008NanoL...8..241W. 
  8. ↑ Güçlü, A. D.; Potasz, P.; Voznyy, O.; Korkusinski, M.; Hawrylak, P. (10 December 2009). "Magnetism and Correlations in Fractionally Filled Degenerate Shells of Graphene Quantum Dots". Physical Review Letters 103 (24): 246805. doi:10.1103/PhysRevLett.103.246805. PMID 20366221. Bibcode: 2009PhRvL.103x6805G. 
  9. ↑ Ortiz, Ricardo; Boto, Roberto A.; García-Martínez, Noel; Sancho-García, Juan C.; Melle-Franco, Manuel; Fernández-Rossier, Joaquı́n (11 September 2019). "Exchange Rules for Diradical π-Conjugated Hydrocarbons". Nano Letters 19 (9): 5991–5997. doi:10.1021/acs.nanolett.9b01773. PMID 31365266. Bibcode: 2019NanoL..19.5991O. 
  10. ↑ Lieb, Elliott H. (6 March 1989). "Two theorems on the Hubbard model". Physical Review Letters 62 (10): 1201–1204. doi:10.1103/PhysRevLett.62.1201. PMID 10039602. Bibcode: 1989PhRvL..62.1201L. 
  11. ↑ Mishra, Shantanu; Beyer, Doreen; Eimre, Kristjan; Liu, Junzhi; Berger, Reinhard; Gröning, Oliver; Pignedoli, Carlo A.; Müllen, Klaus et al. (10 July 2019). "Synthesis and Characterization of π-Extended Triangulene". Journal of the American Chemical Society 141 (27): 10621–10625. doi:10.1021/jacs.9b05319. PMID 31241927. https://boris.unibe.ch/141648/2/Postprint.pdf. 
  12. ↑ Su, Jie; Telychko, Mykola; Hu, Pan; Macam, Gennevieve; Mutombo, Pingo; Zhang, Hejian; Bao, Yang; Cheng, Fang et al. (July 2019). "Atomically precise bottom-up synthesis of π-extended [5triangulene"]. Science Advances 5 (7): eaav7717. doi:10.1126/sciadv.aav7717. PMID 31360763. Bibcode: 2019SciA....5.7717S. 
  13. ↑ Mishra, Shantanu; Xu, Kun; Eimre, Kristjan; Komber, Hartmut; Ma, Ji; Pignedoli, Carlo A.; Fasel, Roman; Feng, Xinliang et al. (2021). "Synthesis and characterization of [7]triangulene". Nanoscale 13 (3): 1624–1628. doi:10.1039/d0nr08181g. PMID 33443270. 
  14. ↑ Mishra, Shantanu; Beyer, Doreen; Eimre, Kristjan; Ortiz, Ricardo; Fernández‐Rossier, Joaquín; Berger, Reinhard; Gröning, Oliver; Pignedoli, Carlo A. et al. (13 July 2020). "Collective All‐Carbon Magnetism in Triangulene Dimers". Angewandte Chemie International Edition 59 (29): 12041–12047. doi:10.1002/anie.202002687. PMID 32301570. 
  15. ↑ Mishra, Shantanu; Catarina, Gonçalo; Wu, Fupeng; Ortiz, Ricardo; Jacob, David; Eimre, Kristjan; Ma, Ji; Pignedoli, Carlo A. et al. (13 October 2021). "Observation of fractional edge excitations in nanographene spin chains". Nature 598 (7880): 287–292. doi:10.1038/s41586-021-03842-3. PMID 34645998. Bibcode: 2021Natur.598..287M. 



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