A new redox‐amphoteric ligand comprising a p‐phenylene‐extended tetrathiafulvalene (TTF) core and two o‐quinone termini has been synthesized. This work was performed in an attempt to synthesize a bridging ligand by combining one of the most powerful organic donors with strong acceptor units in a single molecule. The product was isolated in the doubly reduced diprotonated form. An X‐ray diffraction study revealed a rigid and planar structure for this molecule. This is the first example of an air‐stable p‐phenylene‐extended TTF with an unprotected central ring. The diquinone form itself has been prepared by oxidation of the doubly reduced diprotonated species and then characterized in solution. The electronic spectrum of this compound contains an intense peak that corresponds to intramolecular charge transfer. The spectroscopic and structural studies of both compounds were accompanied by DFT calculations. A singlet biradical ground state was predicted for the doubly reduced diprotonated form.

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.

Chemical reduction of an acceptor–donor–acceptor bis-chelating system: an EPR and UV-vis study.