Bromination of bis(pyridin-2-yl) diselenide in methylene chloride: the reaction mechanism and crystal structures of 1<i>H</i>-pyridine-2-selenenyl dibromide and its cycloadduct with cyclopentene (3a<i>SR</i>,9a<i>RS</i>)-2,3,3a,9a-tetrahydro-1<i>H</i>-cyclopenta[4,5][1,3]selenazolo[3,2-<i>a</i>]pyridinium bromide
Acta crystallographica. Section E, Crystallographic communications