TEMPO Radical-Functionalized Supramolecular Coordination Complexes with Controllable Spin–Spin Interactions

Abstract

The topic of noncovalent spin−spin interactions is of increasing general interest in supramolecular radical chemistry. In this report, a series of exoand endo-TEMPO radical-functionalized metallacycles 1−4 and metallacages 5 and 6 were constructed via coordination-driven selfassembly, wherein the number, location, and distance of the spins were precisely controlled. Their intriguing spin−spin interactions were systematically investigated by electron paramagnetic resonance (EPR) and were well interpreted at the molecular level assisted by X-ray crystallography analysis. The results revealed their distinct spin−spin interactions in the solution state, wherein the spin−spin interaction of metallacycle 3 was much stronger than that of the other five assemblies mainly due to its shorter intramolecular spin−spin distance. In the solid state, 1−6 exhibited obvious spin−spin (dipole−dipole) interactions because of the close arrangement of TEMPO units as indicated in their single crystals. Specifically, a large zero-field splitting (ZFS; D = 17.5 mT) was observed in the crystalline form of metallacycle 4, which arose from the strong intermolecular spin−spin coupling. Interestingly, when the counterion of PF 6 − in 4 was changed to BF 4 − , the BF 4 − counterion analog 4a also exhibited a large ZFS, but the ZFS originated from the intramolecular spin−spin interaction due to a small variation in its crystal conformation. Moreover, the reversible on−off switching of the ZFS in 4 and 4a via the crystal-to-amorphous transformation induced by mechanical grinding and solvent vapor stimuli was also successfully realized. The unique and controllable inter-and intramolecular spin−spin interactions in this work reveal new insights for the understanding and manipulation of spin−spin interactions and may open up a new way to develop organic spin materials in the future.

Activation of Nitrogen-Rich Substrates by Low-Valent, Redox-Active Aluminum Species

“…In this case, the EPR spectrum (Figures S14) also shows the monoradical paramagnetic signal (g = 2.004) at room temperature. 54,55 Variable-temperature EPR measurements show that at 200−300 K the triplet species was hardly observed (Figure S16). The diradical signal intensity at 150 K is enhanced, while the central doublet signal (due to the monoanion) drastically broadened below 200 K because the molecular motion was frozen.…”

Recent advances and perspectives on supramolecular radical cages

“…Recently, we prepared a series of TEMPO radical-functionalized supramolecular coordination complexes including metallacycles and metallacages, wherein the number, location, and distance of the spins were precisely controlled. 10 Their intriguing spin–spin interactions were systematically investigated by EPR and were well interpreted at the molecular level assisted by X-ray crystallography analysis. Particularly, the exo - and endo -TEMPO radical-functionalized cages ( 14 and 15 ) exhibited some distinctive properties.…”

“…Our group has recently engaged in this field and we think that the area of supramolecular radical cages still remains largely unexplored. 10 A large exploration research space exists in this topic. We would like to summarize and highlight the recent progress on the development of supramolecular radical cages regarding their design and synthesis, chemical and physical properties and applications.…”

The First High‐Temperature Supramolecular Radical Ferroics

“…[9] Among them, nearly all the guest ions are organic amine.R ecently,s upramolecular chemistry also extends to the realm of radicals,f or which the weak forces involved in the supramolecular system may control ar adical in an unexpected way. [10] Radical is avital species involving in normal physiological processes,including aerobic metabolism and inflammatory responses,w hile it can also inflict cellular damage,which is closely related to human lifespan. [11] In this context, radicals have long been pursued owing to the significant contribution on polymerization, plasma chemistry, and biochemistry.…”