InChI=1S/C21H16Cl2O7/c1-27-12-6-4-10(5-7-12)15-17(24)19(30-21(15)26)16(20(25)29-3)11-8-13(22)18(28-2)14(23)9-11/h4-9,24H,1-3H3/b19-16+