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2,2′-[(4,6-Dinitro-1,3-phenylene)dioxy]diacetic acid hemihydrate

The skeletons of both independent molecules of the carboxylic acid hemihydrate, C10H8N2O10·0.5H2O, are approximately planar [maximum deviations 0.642 (3) and 0.468 (1) Å]. The deviations arise from the twisting of the nitro groups with respect to the aromatic rings [dihedral angles = 3.24 (2) and 27.01 (1), and 7.87 (1) and 16.37 (2)° in the two molecules]. The crystal structure features intermolecular O—H⋯O hydrogen bonds, which the link the dicarboxylic acid and water molecules into a supramolecular layer network.

The skeletons of both independent molecules of the carboxylic acid hemihydrate, C 10 H 8 N 2 O 10 Á0.5H 2 O, are approximately planar [maximum deviations 0.642 (3) and 0.468 (1) Å ]. The deviations arise from the twisting of the nitro groups with respect to the aromatic rings [dihedral angles = 3.24 (2) and 27.01 (1), and 7.87 (1) and 16.37 (2) in the two molecules]. The crystal structure features intermolecular O-HÁ Á ÁO hydrogen bonds, which the link the dicarboxylic acid and water molecules into a supramolecular layer network.

Comment
Flexible aromatic carboxylic acid with oxygen is a kind of biological activity of the organic carboxylic acid, not only in agriculture, such as plant growth regulators and herbicides it is applied, but also it is important to the synthesis of some organic medicine centre body. Compared with other rigid carboxylic acid ligands, such flexible aromatic carboxylic acid have highly plasticity and spatial configuration of, so it provides a rich and colorful way to identify and assemble for constructing a novel topological network structure with the special physical and chemical properties (Coronado et al., 2000;Gao et al., 2006). In this paper, we report the synthesis and crystal structures of a new flexible aromatic carboxylic acid compound.
In the crystal structure, the skeletons of the two dicarboxylic acid molecules are all approximately co-planar with the largest deviation being 0.642 (3) Å, 0.4681 Å from O8 and O15 for molecule C1-C10 and molecule C11-C20, respectively ( Figure 1). This deviations are caused by the twisting of the nitro groups with the benzene planes.
There are six symmetry-independent 'active' H atoms in the crystal structure, all of them participate in hydrogen bonds, which link the dicarboxylic acid and water molecules into a two-dimensional layer supramolecular network (Table 1, Figure   2).

Experimental
The synthesis of target product is as follows: chlorine acetic acid (51.6 g, 0.54 mol), sodalye(21.8 g, 0.54 mol) were dissolved into 200 ml distilled water with stirring. The mixture was heated to refluxed for 6 h, then the pH value was adjusted to about 2.0 by using 3 M hydrochloric acid. After cooling to the room temperature, 10.8 g (27%) yellow precipitate was obtained.
The 10.8 g above yellow product was dissolved into 100 ml concentrated sulfuric acid with stirring, and then the mixture of nitric acid (9.45 g, 0.15 mol) and sulfuric acid (20.58 g, 0.21 mol) was dropped into the above solution with keeping the reaction trmperature under 0 ° C for 1 h. The mixture was poured into 500 ml water solution. The crude product was recrystallized from 100 ml water solution, 4.2 g yellow needle crystal was obtained (30%).

Refinement
H atoms bound to C atoms were placed in calculated positions and treated as riding on their parent atoms, with C-H = 0.93 Å (aromatic), C-H = 0.97 Å (methylene), and with U iso (H) = 1.2U eq (C). Water H atoms were initially located in a difference Fourier map, but they were treated as riding on their parent atoms with O-H = 0.85 Å and with with U iso (H) = 1.5 U eq (O). Carboxylic H atoms were found in a difference Fourier map, and refined with U iso (H) = 1.5 U eq (O).