2,2′-Dinitro-5,5′-dithiodibenzoic acid

In the title compound, C14H8N2O8S2, the asymmetric unit contains two independent 2,2′-dinitro-5,5′-dithiodibenzoic acid (Dina) molecules with roughly the same conformation. In the crystal structure, strong intermolecular O—H⋯O hydrogen bonds link the organic molecules into a one-dimensional zigzag chain along the a axis. The dihedral angles between the two aromatic rings [109.3 (2) and 103.1 (3)°] are larger than that (88.95°) observed in a structure of the compound with a solvent water molecule [Shefter & Kalman (1969), J. Chem. Soc. D, p. 1027]. Such a difference may be explained by the occurrence of O—H⋯O hydrogen bonds involving the water molecule in the previously reported structure.

In the title compound, C 14 H 8 N 2 O 8 S 2 , the asymmetric unit contains two independent 2,2 0 -dinitro-5,5 0 -dithiodibenzoic acid (Dina) molecules with roughly the same conformation. In the crystal structure, strong intermolecular O-HÁ Á ÁO hydrogen bonds link the organic molecules into a onedimensional zigzag chain along the a axis. The dihedral angles between the two aromatic rings [109.3 (2) and 103.1 (3) ] are larger than that (88.95 ) observed in a structure of the compound with a solvent water molecule [Shefter & Kalman (1969), J. Chem. Soc. D, p. 1027]. Such a difference may be explained by the occurrence of O-HÁ Á ÁO hydrogen bonds involving the water molecule in the previously reported structure.
The author is grateful to Lishui University for financial support.
supplementary materials sup-1 Acta Cryst. (2008). E64, o2051 [ doi:10.1107/S1600536808031620 ] 2,2'-Dinitro-5,5'-dithiodibenzoic acid L.-J. Wang Comment Until now, various flexible carboxylate ligands can often be employed due to their versatile coordination modes and high structural stability. In particular, multi-benzenecarboxylate ligands have been shown to be good building blocks in the design of metal-organic materials (Li et al., 2006;Luo et al., 2007;Gudbjarlson et al., 1991). On the other hand, relative strong hydrogen bondings play an important role in the formation of the ultimate netwrok (Ye et al., 2005). Originally, we attempted to synthesize a complex in the presence of metal salt. However, we only obtain the starting organic material (I).
In the title compound, [C 14 H 8 N 2 O 8 S] 2 , the asymmetric unit is built up by two independent 5,5'-dithiobis(2-nitrobenzcicacid) (Dina) molecules having roughly the same conformation (Fig. 1) (Shefter & Kalman, 1969). In this previous structure, the occurrence of the water molecule which acts as donor and acceptor, links the organic molecules to build up a sheet whereas in the title compound, the O-H···O hydrogen bonds form chains which develop parallel to the a axis (Table 1, Fig.2). In the previously reported compound, [C 14 H 8 the dihedral angles between the two aromatic rings is slightly smaller (88.95°) than in the title compound. Such difference might result from the occurrence of the water molecule which interconnects the oragnic molecule.

Refinement
All H atoms attached to C and O atoms were fixed geometrically and treated as riding with C-H = 0.93 Å (aromatic) and