Mining 2:2 Complexes from 1:1 Stoichiometry: Formation of Cucurbituril−Diarylviologen Quaternary Complexes Favored by Electron-Donating Substituents
Journal of the American Chemical Society
American Chemical Society
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Wu, G., Olesińska, M., Wu, Y., Matak Vinkovic, D., & Scherman, O. (2017). Mining 2:2 Complexes from 1:1 Stoichiometry: Formation of Cucurbituril−Diarylviologen Quaternary Complexes Favored by Electron-Donating Substituents. Journal of the American Chemical Society, 139 (8), 3202-3208. https://doi.org/10.1021/jacs.6b13074
A 1:1 binding stoichiometry of a host−guest complex need not consist of a single host and guest. Diarylviologens containing electron-donating substituents complexed with cucurbituril (CB) in a 1:1 stoichiometry exhibit abnormally large binding enthalpies compared to typical enthalpy changes observed for 1:1 binary complexes. Here, several CB-mediated host−guest complexes, which were previously reported as 1:1 binary complexes, are verified to be 2:2 quaternary complexes by a combination of isothermal titration calorimetry, $^1$H, NOESY, and ROESY NMR, and ion mobility mass spectrometry, clearly indicating a binding motif of two partially overlapping diarylviologens held in place with two CB molecules. Formation of 2:2 quaternary complexes is favored by electron-donating substituents, while electron-withdrawing substituents typically result in 1:1 binary complexes. The stacking of two highly conjugated diarylviologens in one quaternary motif affords the complexes enhanced conductance when considered as a single-molecular conductor. Moreover, an additional conducting signal previously observed for this “supramolecular” conductor can be readily understood with our 2:2 complexation model, corresponding to a parallel conductance pathway. Therefore, a 2:2 quaternary complex model grants a greater understanding of such supramolecular complexes, enabling the design of engineered, hierarchical structures and functional materials.
The authors thank the Leverhulme Trust (project: ‘Natural material innovation for sustainable living’), the Marie Curie FP7 SASSYPOL ITN (607602) programme, and EPSRC (EP/ L504920/1) for funding.
Leverhulme Trust (RP2013-SL-008)
European Commission (607602)
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External DOI: https://doi.org/10.1021/jacs.6b13074
This record's URL: https://www.repository.cam.ac.uk/handle/1810/263745
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