Discrete open-shell tris(bipyridinium radical cationic) inclusion complexes in the solid state

Anamimoghadam, O., Jones, L. O., Cooper, J. A. ORCID: https://orcid.org/0000-0002-3981-9246, Beldjoudi, Y., Nguyen, M. T., Liu, W., Krzyaniak, M. D., Pezzato, C., Stern, C. L., Patel, H. A., Wasielewski, M. R., Schatz, G. C. and Stoddart, J. F. (2021) Discrete open-shell tris(bipyridinium radical cationic) inclusion complexes in the solid state. Journal of the American Chemical Society, 143 (1). pp. 163-175. ISSN 0002-7863 doi: 10.1021/jacs.0c07148

Abstract/Summary

The solid-state properties of organic radicals depend on radical–radical interactions that are influenced by the superstructure of the crystalline phase. Here, we report the synthesis and characterization of a substituted tetracationic cyclophane, cyclobis(paraquat-p-1,4-dimethoxyphenylene), which associates in its bisradical dicationic redox state with the methyl viologen radical cation (MV•+) to give a 1:1 inclusion complex. The (super)structures of the reduced cyclophane and this 1:1 complex in the solid state deviate from the analogous (super)structures observed for the reduced state of cyclobis(paraquat-p-phenylene) and that of its trisradical tricationic complex. Titration experiments reveal that the methoxy substituents on the p-phenylene linkers do not influence binding of the cyclophane toward small neutral guests—such as dimethoxybenzene and tetrathiafulvalene—whereas binding of larger radical cationic guests such as MV•+ by the reduced cyclophane decreases 10-fold. X-ray diffraction analysis reveals that the solid-state superstructure of the 1:1 complex constitutes a discrete entity with weak intermolecular orbital overlap between neighboring complexes. Transient nutation EPR experiments and DFT calculations confirm that the complex has a doublet spin configuration in the ground state as a result of the strong orbital overlap, while the quartet-state spin configuration is higher in energy and inaccessible at ambient temperature. Superconducting quantum interference device (SQUID) measurements reveal that the trisradical tricationic complexes interact antiferromagnetically and form a one-dimensional Heisenberg antiferromagnetic chain along the a-axis of the crystal. These results offer insights into the design and synthesis of organic magnetic materials based on host–guest complexes.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/113512
Item Type	Article
Refereed	Yes
Divisions	No Reading authors. Back catalogue items
Publisher	American Chemical Society
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