[TDNQ][CoCp*₂] and [TDNQ]₃[CoCp₂]₂; Radical Anions of a 1,2,5-Thiadiazolo-naphthoquinone

The first crystal structure of a quinone[1,2,5]thiadiazole radical anion is presented. Reduction of naphtha[2,3-c][1,2,5]thiadiazole-4,9-dione (TDNQ) with outersphere electron transfer agents, decamethylcobaltocene (CoCp*2) and cobaltocene (CoCp2), by slow mixing of solutions, generates two species: [TDNQ][CoCp*2] and [TDNQ]3[CoCp2]2, respectively. The [TDNQ][CoCp*2] is soluble in a wide variety of organic solvents, whereas [TDNQ]3[CoCp2]2 is generally insoluble. The radical anion oxidation state, TDNQ•, in [TDNQ][CoCp*2] is confirmed by lengthened C–O bond distances in the (solvated) crystal structure, as compared to neutral TDNQ, shifting of the ν(C–O) stretch in the IR absorption spectrum, and the presence of a solution electron paramagnetic resonance (EPR) signal. In the [TDNQ]3[CoCp2]2 species, copacking of single-molecule radical anions, TDNQ•, and bimolecular radical anion units, (TDNQ)2•, with cobaltocenium cations is observed. The magnetic measurements highlight the presence of dominating antiferromagnetic interactions between TDNQ• and (TDNQ)2• spins in this cobaltocene salt.