In 5-iodoisatin (5-iodo-1H-indole-2,3-dione), C8H4INO2, the molecules are linked into chains of rings by N-H...O and C-H...O hydrogen bonds, and these chains are linked into sheets by iodo-carbonyl interactions. In 7-trifluoromethylisatin (7-trifluoromethyl-1H-indole-2,3-dione), C9H4F3NO2, the molecules are linked into sheets of centrosymmetric R(2)2(8) and R(6)6(34) rings by N-H...O and C-H...O hydrogen bonds.