Chemistry of N-heterocyclic sulfur compounds. Reaction of 2,5-dimercapto-1,3,4-thiadiazoles with 1,.omega.-dibromoalkanes. Synthesis of tetrathia[(n + 2).(n + 2)](2,5)-1,3-4-thiadiazolophanes and dithia[(n + 1).(n + 1)](3,5)-1,3,4-thiadiazolinophanedithiones