The X-ray single-crystal structure determinations of the chemically related compounds 2-amino-1,3,4-thiadiazolium hydrogen oxalate, C2H4N3S+ C2HO4 , (I), 2-amino-1,3,4-thiadiazole- succinic acid (1/2), C2H3N3S 2C4H6O4, (II), 2-amino-1,3,4-thiadiazole-glutaric acid (1/1), C2H3N3S - C5H8O4, (III), and 2-amino-1,3,4-thiadiazole-adipic acid (1/1), C2H3N3S C6H10O4, (IV), are reported and their hydrogenbonding patterns are compared.