A simple triangular multi-redox pseudo-[6]oxocarbon capable of accepting up to six electrons

Multi-electron redox chemistry is traditionally a domain of transition metals which are well-known to show multiple valence states with a vast variation of physical and chemical properties. Redox-active organic molecules, on the other hand, usually present only two valence states. Herein we demonstrate the design and preparation of a very simple organic molecule benzo[1,2-c:3,4-c':5,6-c'']tris([1,2,5]thiadiazole) 2,2,5,5,8,8-hexaoxide (tripak) that shows unprecedently rich redox chemistry and is capable of accepting up to six electrons in five consecutive reduction steps. Tripak is a derivative of the thermodynamically unstable [6]oxocarbon C6O6, where all C=O groups were used to form three dioxothiadiazole rings. It is the first representative of the new poly(dioxothiadiazole) family of compounds comprising three dioxothiadiazole groups fused together to form a simple rigid highly symmetrical skeleton with a single benzenoid ring in the middle. The electron withdrawing character of the dioxothiadiazole rings is responsible for the reversible multi-electron redox behavior which enabled its isolation and complete structural and physicochemical characterization in five-out-of-six oxidation states: 0, -1, -2, -3 and -4. Depending on the number of electrons, the tripak system represents different types of aromaticity (non-aromatic, Hückel or Baird) and redox-related multifunctionality: tripak0 shows record-strong anion-π binding of halides which is comparable with the energy of coordination bonds, tripak1- and tripak3- are two very different S = 1/2 radical states with tripak1- exhibiting very long spin-spin relaxation time at room temperature placing it among the most promising molecular qubit candidates, tripak2- is a blue dye with strong red fluorescence and finally tripak4- is an open-shell singlet diradicaloid system with a singlet-triplet gap close to zero.