Dimethyl 5-amino-2,4,6-triiodo-isophthalate.

The title compound, C(10)H(8)I(3)NO(4), crystallizes with two mol-ecules in the asymmetric unit. The I atoms and the benzene ring plane in the two mol-ecules are approximately coplanar, the I atoms deviating by -0.1631 (1), 0.0704 (1) and -0.0507 (1) Å from the mean plane of the benzene ring in one mol-ecule and by 0.1500 (1), -0.0034 (1) and -0.1213 (1) Å in the other. The planes of the ester groups are almost orthogonal to those of the benzene rings in both mol-ecules, forming dihedral angles of 83.5 (3), 76.4 (3), 97.3 (1) and 75.7 (1)°. The mean planes of the benzene rings in two mol-ecules are inclined at 69.8 (3)° with respect to each other. In the crystal, inter-molecular I⋯O inter-actions link the mol-ecules into infinite chains. In addition, N-H⋯O and non-classical C-H⋯O hydrogen bonds are observed.

The title compound, C 10 H 8 I 3 NO 4 , crystallizes with two molecules in the asymmetric unit. The I atoms and the benzene ring plane in the two molecules are approximately coplanar, the I atoms deviating by À0.1631 (1), 0.0704 (1) and À0.0507 (1) Å from the mean plane of the benzene ring in one molecule and by 0.1500 (1), À0.0034 (1) and À0.1213 (1) Å in the other. The planes of the ester groups are almost orthogonal to those of the benzene rings in both molecules, forming dihedral angles of 83.5 (3), 76.4 (3), 97.3 (1) and 75.7 (1) . The mean planes of the benzene rings in two molecules are inclined at 69.8 (3) with respect to each other. In the crystal, intermolecular IÁ Á ÁO interactions link the molecules into infinite chains. In addition, N-HÁ Á ÁO and nonclassical C-HÁ Á ÁO hydrogen bonds are observed.

Comment
The 1,3,5-triiodobenzene core has been the basis of many contrast agents (Yu & Watson, 1999). The title compound is useful as an important intermediate for the preparation of iodinated X-ray contrast agent, such as iotalamic acid, ioxitalamic acid, and ioxilan, which are used clinically all over the world (Morin et al., 1987;Singh et al., 1980;Stacul et al., 2001). In this paper, we present the crystal structure of the title compound.
The asymmetric unit of the title compound ( Fig. 1) contains two crystallographically independent molecules (A and B) in an asymmetric unit. The three I atoms deviate from the mean-planes of the phenyl rings, respectively, by -0.1631 (1), 0.0704 (1) and -0.0507 (1) Å for molecule A and 0.1500 (1), -0.0034 (1) and -0.1213 (1) Å for molecule B. Bond lengths and angles are comparable to those observed in a related structure (Beck & Sheldrick, 2008). The planes of the ester groups in In the crystal structure, intermolecular I···O interactions link the molecules into infinite one-dimensional chains (Fig. 2).
In addition, C-H···O hydrogen bonds and N-H···O hydrogen bonds are observed.

Refinement
All H atoms were initially located from a difference Fourier map and then were regenerated at ideal positions and treated as riding, with N-H = 0.88 Å, C-H = 0.98 Å and U iso (H) = 1.2U eq (N), U iso (H) = 1.5U eq (C). The final difference map showed electron density in the vicinity of I3B atom and was deemed meaningless.