Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

Abstract

The chemical oxidation and reduction processes of deprotonated, direduced o-quinone-exTTF-o-quinone in protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone–quinone and semiquinone–catechol redox forms indicates that the p-phenylene-extended tetrathiafulvalene connector provides a quite effective electronic communication channel between dioxolene coordination sites. It was found that the deprotonated, direduced o-quinone-exTTF-o-quinone is capable to reduction of the metal copper in solution. The radical anion species formed in this reaction exists in solution as a solvent-separated ion pair with a copper cation. A character of spin-density distribution in a radical anion species leads to the conclusion that the ligand corresponds to type III of the Robin–Day classification.

Field-Induced Dysprosium Single-Molecule Magnet Involving a Fused o-Semiquinone-Extended-Tetrathiafulvalene-o-Semiquinone Bridging Triad

“…The value of the antiferromagnetic coupling between the two semiquinone radical centers was estimated as 1092 cm −1 [23]. Consequently the biradical triad L is Electronic Paramagnetic Resonance (EPR) silent [23].…”

“…This triad was previously studied by open-shell density functional theory calculations, which revealed that the broken-symmetry (BS) state in a global minimum is singlet biradical according to the spin density distribution. The value of the antiferromagnetic coupling between the two semiquinone radical centers was estimated as 1092 cm −1 [23]. Consequently the biradical triad L is Electronic Paramagnetic Resonance (EPR) silent [23].…”

“…The value of the antiferromagnetic coupling between the two semiquinone radical centers was estimated as 1092 cm −1 [23]. Consequently the biradical triad L is Electronic Paramagnetic Resonance (EPR) silent [23]. The coordination reaction between an equimolar ratio of the [Dy(hfac)3]·2H2O metallo-precursor and the L triad leads to the formation of dark blue-purple single crystals of {[Dy(hfac)3(L)]·2C6H14}n (1) after the slow diffusion of n-hexane in the dark.…”

Functionalized o-Quinones: Concepts, Achievements and Prospects

“…Interaction of 68 with an excess of Mn 2 (CO) 10 results in subsequent formation of semiquinonate 69 and then the trinuclear species 70 (Scheme 30) [42]. Mononuclear semiquinonate 69 has a sextet lines EPR spectrum in toluene due to splitting of the unpaired electron on the 55 Mn nucleus (Figure 3a). A multiplet spectrum that arises upon further reduction of 69 with Mn 2 (CO) 10 was attributed to the trinuclear species 70.…”

“…Mononuclear semiquinonate 69 has a sextet lines EPR spectrum in toluene due to splitting of the unpaired electron on the 55 Mn nucleus (Figure 3a). A multiplet spectrum that arises upon further reduction of 69 with Mn2(CO)10 was attributed to the trinuclear species 70.…”