Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State

Abstract

Thermally resistant air-stable organic triradicals with a quartet ground state and a large energy gap between spin states are still unique compounds. Moreover, stable triradicals with bridging units of the ethylene-1,1-diyl type and ferromagnetic coupling are limited to the family of nitroxides. In this work, for the first time, we designed and prepared the triradical having a quartet ground state based on oxoverdazyl and nitronyl nitroxide radical fragments. The triradical and appropriate triplet diradical precursor were synthesized via a palladium-catalyzed cross-coupling reaction of diiodoverdazyl with nitronyl nitroxide-2-ide gold(I) complex. Both the di-and triradical are air-stable and possess good thermal stability with decomposition onset at ∼160 °C in an inert atmosphere. X-ray diffraction analysis of single crystals confirmed the presence of verdazyl and nitroxide radical centers. In the diradical, the verdazyl and nitronyl nitroxide centers showed fully reversible redox waves. In case of the triradical, the electrochemical processes occur practically at the same redox potentials but become quasi-reversible for the nitroxide moieties. Magnetic properties of the di-and triradical were characterized by a SQUID magnetometry of polycrystalline powders and by EPR spectroscopy in different matrices. Collected data analyzed using of the highlevel quantum chemical calculations confirmed that the di-and triradical have high-spin ground states. Unique high stability of prepared verdazyl-nitronylnitroxyl triradical opens new perspectives for further functionalization and design of high-spin systems with four or more spins.

High-Spin (S = 1) Blatter-Based Diradical with Robust Stability and Electrical Conductivity

“…Here, we report the synthesis, characterization, and thin film preparation of di-Blatter diradical 4 . The diradical possesses a triplet ground state and robust thermal stability, with an onset of decomposition above 264 °Cthe highest temperature among high-spin diradicals or triradicals studied by TGA. ,,− …”

Cyclopenta-fused polyaromatic hydrocarbons: synthesis and characterisation of a stable, carbon-centred helical radical

“…The values obtained in CH 2 Cl 2 suggest that three reductions (1–3) and two oxidations (4, 5) are possible for 7 . In addition, an electrochemical SOMO–LUMO gap can be deduced from these values: 32 E SOMO : −(4.8 + E 0 1/2 (4, CH 2 Cl 2 )) eV = −(4.8 + 1.11) eV = −5.91 eV; E LUMO : −(4.8 + E 0 1/2 (3, CH 2 Cl 2 )) eV = −(4.8 − 0.16) eV = −4.64 eV. The thus obtained gap of 1.27 eV is reasonably close to the optical gap obtained from TD calculations (1.17 eV, vide infra ).…”

Multispin Systems with a Rigid Ferrocene‐1,1′‐diyl‐Substituted 1,3‐Diazetidine‐2,4‐diimine Coupler: A General Approach

“…In addition to these peaks, the cyclic voltammogram of 7 c also contains an irreversible oxidation event at 1.07 V, which can be ascribed either to the oxidation of the Ph−O−CH 3 moiety or to trace amounts of impurities/degradation products present in the sample. The reduction of the NO 2 group in the 7 d radical manifests itself at −1.64 V. The CV of diradical 8 a , in addition to electrochemical events related to the Fc and nitroxide parts, revealed reversible peaks of oxidation (E 1/2 ≈0.36 V) and reduction (E 1/2 ≈−1.46 V) resulting from oxidation/reduction of the nitronyl nitroxide moiety [24] . For 8 b , the corresponding oxidation event for the nitronyl nitroxide moiety seems to be very close to that for the nitroxide moiety (Table 2 and Figure 7), and quasi‐reversible reduction appears near −1.57 V.…”

“…The reduction of the NO 2 group in the 7 d radical manifests itself at À 1.64 V. The CV of diradical 8 a, in addition to electrochemical events related to the Fc and nitroxide parts, revealed reversible peaks of oxidation (E 1/2 � 0.36 V) and reduction (E 1/2 � À 1.46 V) resulting from oxidation/reduction of the nitronyl nitroxide moiety. [24] For 8 b, the corresponding oxida- tion event for the nitronyl nitroxide moiety seems to be very close to that for the nitroxide moiety (Table 2 and Figure 7), and quasi-reversible reduction appears near À 1.57 V. Figure 8 presents the EPR spectra of radicals 7 a and 7 e recorded for diluted (c � 10 À 4 M) oxygen-free solutions at 295 K. Both spectra consist of three lines due to hyperfine coupling (hfc) with nitrogen nuclei. The difference in line broadening between these spectra can be explained by incomplete averaging of the hfc and g-tensor anisotropy.…”