Two derivatives of 4- chloro -2,2 ′ -iminodibenzoic acid: diethyl 4- chloro -2,2 ′ -iminodibenzoate, C 18 H 18 ClNO 4 , and dimethyl 4- chloro -2,2 ′ -iminodibenzoate C 16 H 14 ClNO 4 , have been investigated by means of X-ray powder diffraction. The unit cell dimensions were determined from diffractometer methods, using monochromatic CuK α 1 radiation, and evaluated by indexing programs. The monoclinic cell found for diethyl 4- chloro -2,2 ′ -iminodibenzoate was a =21.332(3) Å, b =7.889(2) Å, c =10.156(2) Å, β=91.43(1)°, Z =4, space group P 2 (No. 3), Pm (No. 6), or P 2/ m (No. 10), D x =1.351 mg / m 3 . The cell found for this compound is in good agreement with the one obtained from single crystal X-ray diffractometry. The monoclinic cell found for dimethyl 4- chloro -2,2 ′ -iminodibenzoate has the dimensions a =15.962(2) Å, b =5.151(2) Å, c =12.590(2) Å, β=98.35(1)°. Z =4, space group P 2 (No. 3), Pm (No. 6), or P 2/ m (No. 10), D x =2.073 mg / m 3 .