3D global aromaticity in a fully conjugated diradicaloid cage at different oxidation states

Abstract

Aromaticity is a vital concept that governs the electronic properties of π-conjugated organic molecules and has long been restricted to 2D systems. The aromaticity in 3D π-conjugated molecules has been rarely studied. Here we report a fully conjugated diradicaloid molecular cage and its global aromaticity at different oxidation states. The neutral compound has an open-shell singlet ground state with a dominant 38π monocyclic conjugation pathway and follows the [4n + 2] Hückel aromaticity rule; the dication has a triplet ground state with a dominant 36π monocyclic conjugation pathway and satisfies [4n] Baird aromaticity; the tetracation is an open-shell singlet with 52 π-electrons that are delocalized along the 3D rigid framework, showing 3D global antiaromaticity; and the hexacation possesses D3 symmetry with 50 globally delocalized π-electrons, showing [6n + 2] 3D global aromaticity. Different types of aromaticity were therefore accessed in one molecular cage platform, depending on the symmetry, number of π-electrons and spin state.

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Fig. 1: The design of a 3D π-conjugated diradical cage and synthesis of c-T12.
Fig. 2: Electrochemical and optical properties.
Fig. 3: X-ray crystallographic structures.
Fig. 4: Theoretical calculations and π-electron delocalization diagrams of c-T12, c-T122+, c-T124+ and c-T126+ in ground state.
Fig. 5: 1H NMR (500 MHz) spectra of c-T12 at different oxidation states.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information. Output files of the optimized geometries of c-T12, c-T122+, c-T124+, c-T126+ and c-T12′6+ in their respective ground states are available as Supplementary Data. Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition nos. CCDC 1907315 (c-T12), 1907316 (c-T122+), 1907317 (c-T124+), 1907318 (c-T125+) and 1907319 (c-T126+). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/.

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Acknowledgements

J.W. acknowledges financial support from the MOE Tier 3 programme (grant no. MOE2014-T3-1-004) and NRF Investigatorship (grant no. NRF-NRFI05-2019-0005). We thank S. Tobias and H. Ott from Brucker for their support on X-ray diffraction data collection. We also thank Z. Chen in the University of Puerto Rico for his helpful discussion.

Author information

J.W. and Y.N. conceived the project. Y.N. synthesized the compounds and collected the spectral data. T.Y.G. performed theoretical calculations. Y.N., T.S.H., H.P. and J.D. did magnetic measurements and analysis. Y.N., Y.H. and T.T. did the X-ray analysis. T.K. and D.K. did the transient absorption spectral measurement and analysis. All authors participated in the manuscript writing.

Correspondence to Jishan Wu.

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Competing interests

The authors declare no competing interests.

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Supplementary information

Supplementary information

Experimental methods, synthetic procedures and characterization data. Details of theoretical calculations and X-ray crystallographic analysis.

Crystallographic data

CIF for compound c-T12; CCDC reference: 1907315.

Crystallographic data

CIF for compound c-T122+; CCDC reference: 1907316.

Crystallographic data

CIF for compound c-T124+; CCDC reference: 1907317.

Crystallographic data

CIF for compound c-T125+; CCDC reference: 1907318.

Crystallographic data

CIF for compound c-T126+; CCDC reference: 1907319.

Computational data

Output files of the optimized geometries of c-T12, c-T122+, c-T124+, c-T126+ and c-T12′6+ in their respective ground states. Note that c-T12′6+ is an analogue of c-T126+ in which the Mes groups are replaced by hydrogen atoms.

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Ni, Y., Gopalakrishna, T.Y., Phan, H. et al. 3D global aromaticity in a fully conjugated diradicaloid cage at different oxidation states. Nat. Chem. (2020). https://doi.org/10.1038/s41557-019-0399-2

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