Electron spin resonance studies of radicals derived from dithionate, tetrathionate, and thiosulphate anions
Abstract
Exposure of sodium dithionate to 60Co γ-rays at 77 K gives a centre having hyperfine coupling to 33S (A∥= 165 G, A⊥= 135 G) which is thought to be the primary electron-capture centre [S2O6]3– having the extra electron confined to the S–S σ* orbital. This assignment is supported by the observation that 33S features characteristic of [33SO3]– radicals grew in as those assigned to [S2O6]3– anions were lost on annealing. The major electron-loss centre is identified as the hydroxyl radical formed from hydrate water molecules. Sodium thiosulphate gives a radical having a large isotropic hyperfine coupling to 33S. This centre, previously thought to be [S2O3]–, is now identified as [S2O3]3–. In anhydrous Na2[S2O3] this centre exhibits hyperfine coupling to 23Na. This salt and K2[S2O3]·5H2O give a new species having one very high g value, identified as [S2O3]–. Two sets of 33S features are obtained from [S2O6]3– suggesting an asymmetric environment. In accord with this, two slightly different [˙SO3]– radicals are obtained on annealing. The anion [O3SS–SSO3]3– is a primary product in irradiated sodium tetrathionate, but is not detected in thiosulphate even after annealing. A second centre formed from tetrathionate exhibits a large g value variation and extra hyperfine coupling to 23Na.