Die Kristallstrukturen des Benzo1.2-c:3.4-cʹbis1.2.5thiadiazols und des semihomologen 1.2.5Selenadiazolo3.4-e-2.1.3-benzothiadiazols 1/The Crystal Structures of the Benzo 1,2-c : 3,4-cʹbis1,2,5thiadiazole and of the Semihomologous 1,2,5Selenadiazolo3,4-e-2,1,3-benzothiadiazole 1