Electron paramagnetic resonance study of S3− formed on magnesium oxide

Elemental sulfur reacts at 400° with partially hydroxylated magnesium oxide to form a stable paramagnetic species which has been identified as the S3− ion. The 33S hyperfine splitting is characteristic of an aba type molecule with a‖ (a)=20.7 G, a‖ (b)=39.6G, a⊥ (a)=3.7 G, and a⊥ (b)=7.5G. The principal g values are g‖=2.004 and g⊥=2.043. The g and hyperfine tensors suggest that at 77°K the molecule is librating in the plane of the three sulfur atoms. The formation of S3− is accompanied by the evolution of H2S and the loss of another sulfur radical which is believed to be a polymeric form of sulfur, Sn. These observations suggest that the reaction Sn+4OH−→ 2H2S+2S3−+SO4−+Sn-6 may occur at the surface.