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C–H···π interactions disrupt electrostatic interactions between non-aqueous electrolytes to increase solubility

Nature Chemistry volume 15, pages 1365–1373 (2023)Cite this article

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Abstract

Grid-scale energy storage applications, such as redox flow batteries, rely on the solubility of redox-active organic molecules. Although redox-active pyridiniums exhibit exceptional persistence in multiple redox states at low potentials (desirable properties for energy storage applications), their solubility in non-aqueous media remains low, and few practical molecular design strategies exist to improve solubility. Here we convey the extent to which discrete, attractive interactions between C–H groups and π electrons of an aromatic ring (C–H···π interactions) can describe the solubility of N-substituted pyridinium salts in a non-aqueous solvent. We find a direct correlation between the number of C–H···π interactions for each pyridinium salt and its solubility in acetonitrile. The correlation presented in this work highlights a consequence of disrupting strong electrostatic interactions with weak dispersion interactions, showing how minimal structural change can dramatically impact pyridinium solubility.

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Fig. 1: Comparison of strategies for improving electrolyte solubility in non-aqueous solvent.
Fig. 2: Synthesis and non-aqueous solubility of pyridinium ROMs.
Fig. 3: Experimental pyridinium redox potentials enable validation of DFT-optimized structures.
Fig. 4: Conventional physical organic molecular descriptors do not correlate with pyridinium solubility.
Fig. 5: C–H···π interactions increase pyridinium solubility by disrupting ionic crystal lattice.
Fig. 6: 1H-NMR confirms C–H···π interactions are present between solvated pyridiniums.

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Data availability

All data generated or analysed during this study are included in this published article (and its supporting information files) with the exception of raw voltammetry data and raw spectrophotometry data, which can be provided upon request. Metrical parameters for crystal structures are available free of charge from the Cambridge Crystallographic Data Centre under reference numbers CCDC-2162134, 2163981, 2165226, 2157789, 2155765, 2155982, 2162102, 2156178, 2163473, 2155992, 2155704, 2156211, 2156206, 2155715, 2167771, 2157809, 2166708, 2168227, 2157813, 2156563, 2156214 and 2158012. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. Source data are provided with this paper.

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Acknowledgements

We thank the Michigan State University Center for Crystallographic Research for crystallographic analysis and the Michigan State University Mass Spectrometry and Metabolomics Core for providing high-resolution mass spectra of pyridinium salts. The Rigaku Synergy S Diffractometer was purchased with support from the MRI program by the National Science Foundation under grant no. 1919565 for use at the Center for Crystallographic Research, MSU. Portions of this project were made possible by a grant from the Community Foundation of Holland/Zeeland and Lakeshore Advantage through a Michigan Strategic Fund grant (T.G. and C.H.).

Author information

Authors and Affiliations

  1. Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI, USA

    Sharmila Samaroo, Chase Bruggeman, Nunzio Giorgio G. Carducci, Lincoln Mtemeri & David P. Hickey

  2. Michigan State University Bioeconomy Institute, Michigan State University, Holland, MI, USA

    Charley Hengesbach & Thomas Guarr

  3. Department of Chemistry, Michigan State University, East Lansing, MI, USA

    Richard J. Staples

  4. Jolt Energy Storage Technologies, LLC, Holland, MI, USA

    Thomas Guarr

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Contributions

S.S., T.G. and D.P.H. were responsible for the conceptualization of the project. C.H. performed all synthetic procedures. S.S. performed all solubility measurements and crystal growth. L.M. and D.P.H. performed all DFT calculations. R.J.S. collected and analysed all the crystallographic data. S.S., C.H., C.B. and N.G.G.C. analysed and interpreted the experimental and computational data. S.S., C.H., L.M. and D.P.H. prepared the Supplementary Information. S.S. and D.P.H. drafted the original version of the manuscript. All authors contributed to reviewing and editing the final manuscript.

Corresponding authors

Correspondence to Thomas Guarr or David P. Hickey.

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Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Chemistry thanks Magdaléna Hromadova, Steve Scheiner and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 C-H···π interactions correlate with pyridinium solubility in several aprotic solvents.

Plots comparing solubilities of nine representative pyridinium derivatives from low (1, 2, 6, 16), moderate (5, 10, 12, 20) and high (14) solubility regimes (in acetonitrile). Solubilities were evaluated in acetonitrile (blue circles), THF (purple diamonds), cyclohexanone (green triangles), and propylene carbonate (orange squares). (A) A plot comparing pyridinium solubility in each solvent to a descriptor of C-H···π interactions (∑d−6). (B) Semi-log plot of pyridinium solubility in each solvent vs. the dielectric constant of the respective solvent (that is, εTHF = 7.6, εcyclohexanone = 18, εacetonitrile = 37, and εPC = 66). Solubility measurements were performed at 22 °C. Average values are reported where error bars represent one standard deviation with n = 3 for all compounds except for compound 17 (n = 2), compound 24 (n = 5), and compound 14 (n = 9).

Source data

Supplementary information

Supplementary Information

Supplementary materials and methods, text, Figs. 1–97 and Tables 1–6.

Supplementary Data 1

Crystallographic data for compound 1; CCDC reference 2157789.

Supplementary Data 2

Crystallographic data for compound 2; CCDC reference 2156178.

Supplementary Data 3

Crystallographic data for compound 4; CCDC reference 2156211.

Supplementary Data 4

Crystallographic data for compound 5; CCDC reference 2167771.

Supplementary Data 5

Crystallographic data for compound 6; CCDC reference 2155765.

Supplementary Data 6

Crystallographic data for compound 7; CCDC reference 2163473.

Supplementary Data 7

Crystallographic data for compound 8; CCDC reference 2157813.

Supplementary Data 8

Crystallographic data for compound 9; CCDC reference 2156206.

Supplementary Data 9

Crystallographic data for compound 10; CCDC reference 2157809.

Supplementary Data 10

Crystallographic data for compound 11; CCDC reference 2155982.

Supplementary Data 11

Crystallographic data for compound 12; CCDC reference 2155992.

Supplementary Data 12

Crystallographic data for compound 13; CCDC reference 2156563.

Supplementary Data 13

Crystallographic data for compound 14; CCDC reference 2155715.

Supplementary Data 14

Crystallographic data for compound 15; CCDC reference 2166708.

Supplementary Data 15

Crystallographic data for compound 16; CCDC reference 2162102.

Supplementary Data 16

Crystallographic data for compound 17; CCDC reference 2155704.

Supplementary Data 17

Crystallographic data for compound 18; CCDC reference 2156214.

Supplementary Data 18

Crystallographic data for compound 19; CCDC reference 2158012.

Supplementary Data 19

Crystallographic data for compound 20; CCDC reference 2168227.

Supplementary Data 20

Crystallographic data for compound 21; CCDC reference 2162134.

Supplementary Data 21

Crystallographic data for compound 22; CCDC reference 2163981.

Supplementary Data 22

Crystallographic data for compound 23; CCDC reference 2165226.

Supplementary Data 1

Crystallographic structure factor data for compound 1; CCDC reference 2157789.

Supplementary Data 2

Crystallographic structure factor data for compound 2; CCDC reference 2156178.

Supplementary Data 3

Crystallographic structure factor data for compound 4; CCDC reference 2156211.

Supplementary Data 4

Crystallographic structure factor data for compound 5; CCDC reference 2167771.

Supplementary Data 5

Crystallographic structure factor data for compound 6; CCDC reference 2155765.

Supplementary Data 6

Crystallographic structure factor data for compound 7; CCDC reference 2163473.

Supplementary Data 7

Crystallographic structure factor data for compound 8; CCDC reference 2157813.

Supplementary Data 8

Crystallographic structure factor data for compound 9; CCDC reference 2156206.

Supplementary Data 9

Crystallographic structure factor data for compound 10; CCDC reference 2157809.

Supplementary Data 10

Crystallographic structure factor data for compound 11; CCDC reference 2155982.

Supplementary Data 11

Crystallographic structure factor data for compound 12; CCDC reference 2155992.

Supplementary Data 12

Crystallographic structure factor data for compound 13; CCDC reference 2156563.

Supplementary Data 13

Crystallographic structure factor data for compound 14; CCDC reference 2155715.

Supplementary Data 14

Crystallographic structure factor data for compound 15; CCDC reference 2166708.

Supplementary Data 15

Crystallographic structure factor data for compound 16; CCDC reference 2162102.

Supplementary Data 16

Crystallographic structure factor data for compound 17; CCDC reference 2155704.

Supplementary Data 17

Crystallographic structure factor data for compound 18; CCDC reference 2156214.

Supplementary Data 18

Crystallographic structure factor data for compound 19; CCDC reference 2158012.

Supplementary Data 19

Crystallographic structure factor data for compound 20; CCDC reference 2168227.

Supplementary Data 20

Crystallographic structure factor data for compound 21; CCDC reference 2162134.

Supplementary Data 21

Crystallographic structure factor data for compound 22; CCDC reference 2163981.

Supplementary Data 22

Crystallographic structure factor data for compound 23; CCDC reference 2165226.

Source data

Source Data Fig. 2

Pyridinium solubilities in acetonitrile.

Source Data Fig. 3

Representative cyclic voltammograms. Experimentally determined reduction potentials. Experimentally versus computationally determined reduction potentials.

Source Data Fig. 4

Pyridinium solubilities in acetonitrile versus polarizability. Pyridinium solubilities in acetonitrile versus dipole moment. Pyridinium solubilities in acetonitrile versus sterimol parameters. Pyridinium solubilities in acetonitrile versus average distance between N+ and B−.

Source Data Fig. 5

Pyridinium solubilities in acetonitrile versus CH–π parameter.

Source Data Fig. 6

Variable concentration H-NMR peak change for compound 14. Variable concentration H-NMR peak change for compound 13.

Source Data Extended Data Fig.1/Table 1

Pyridinium solubilities in acetonitrile, cyclohexanone, PC and THF versus CH−π parameter. Pyridinium solubilities in acetonitrile, cyclohexanone, PC and THF versus solvent dielectric constant.

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Samaroo, S., Hengesbach, C., Bruggeman, C. et al. C–H···π interactions disrupt electrostatic interactions between non-aqueous electrolytes to increase solubility. Nat. Chem. 15, 1365–1373 (2023). https://doi.org/10.1038/s41557-023-01291-1

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