Early alkali metal (Li, Na, K) and tris(dimethylamino)sulfonium (TAS) salts of [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion:: Rational syntheses, structures and magnetic properties

Salts of the [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (1) and the early alkali metals, [Li(12-crown-4)(2)][1] (3), [Na(15-crown-5)][1] (4), and [K(18-crown-6)][1] (5) as well as the salt [(Me2N)(3)S][1] (6) can be prepared by reduction of [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (2) with PhS- anion followed by XRD and ESR characterization. These salts are thermally stable and soluble in MeCN. Low-temperature crystallization of salt 5 from MeCN or storage of 5 under MeCN for a few days at ambient temperature gives the solvate 5-MeCN (7). The radical anion 1 acts as bridging ligand in salts 4 and 5 and as chelating ligand in salt 7. In salt 3, the radical anion 1 is not coordinated to the cation and can be considered as "naked" anion. In salt 6, one of the two crystallographically independent 1 acts as bridging ligand, whilst the other is not coordinated to the cation. Magnetic susceptibility data obtained for salts 4 and 5 in the temperature range of 2-300 K revealed antiferromagnetic exchange interactions between paramagnetic centers: 4, J = -3.42, aJ = -1.12 cm(-1); 5, J = -1.22 cm(-1).