Different tautomeric and zwitterionic forms of chelidamic acid (4-hydroxypyridine-2, 6- dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C7H5NO5· CH4O,(Ia), dimethylammonium chelidamate (dimethylammonium 6-carboxy-4-hydroxypyridine-2-carboxylate), C2H8N+· C7H4NO5−,(Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C7H5NO5· C2H6OS,(Ic). While the zwitterionic ...