An ESR study of UV-irradiated solutions of tetramethylammonium mercaptoundecahydro-closo-dodecaborate(2-) at 77 K

Abstract

The superoxide anion-radicals O2·- are generated by the ultraviolet irradiation of air- or oxygen-saturated aqueous solutions of tetramethylammonium mercaptoundecahydro-closo-dodecaborate(2-) at 77 K. The superoxide anion-radicals are formed from the oxygen molecule coordinated on the mercaptoundecahydro-closo-dodecaborate dianion. In the absence of this dianion no O2·- are generated. By the irradiation in the presence of hydrogen peroxide the formation of the superoxide anion-radicals is more intensive than in the presence of oxygen only. Simultaneously with O2·- generation the corresponding thiol radicals are formed. These radicals give the disulfide compound [B12H11S]24-. A possible role of sulfur-centered radicals in the autoxidation transformations of the mercaptoundecahydro-closo-dodecaborate dianion is discussed.