Discrete Open-Shell Tris(bipyridinium radical cationic) Inclusion Complexes in the Solid State

Ommid Anamimoghadam, Leighton O. Jones, James A. Cooper, Yassine Beldjoudi, Minh T. Nguyen, Wenqi Liu, Matthew D. Krzyaniak, Cristian Pezzato, Charlotte L. Stern, Hasmukh A. Patel, Michael R. Wasielewski, George C. Schatz, J. Fraser Stoddart*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)163-175
Number of pages13
JournalJournal of the American Chemical Society
Volume143
Issue number1
DOIs
StatePublished - Jan 13 2021

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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