2,2′-Diamino-4,4′-bi-1,3-thiazolium bis(3-nitrobenzoate)

In the title salt, C6H8N4S2 2+·2C7H4NO4 −, the diprotonated diaminobithiazole dication is located on an inversion center. The carboxylate group of the anion is twisted with respect to the benzene ring, with a dihedral angle of 13.6 (4)°. N—H⋯O hydrogen bonds involving the amino and ammonium groups of the dication and the carboxylate functionality of the anion generate supramolecular chains in the crystal.

In the title salt, C 6 H 8 N 4 S 2 2+ Á2C 7 H 4 NO 4 À , the diprotonated diaminobithiazole dication is located on an inversion center. The carboxylate group of the anion is twisted with respect to the benzene ring, with a dihedral angle of 13.6 (4) . N-HÁ Á ÁO hydrogen bonds involving the amino and ammonium groups of the dication and the carboxylate functionality of the anion generate supramolecular chains in the crystal.

Comment
Transition metal complexes of 2,2'-diamino-4,4'-bi-1,3-thiazole (DABT) have shown potential applications in the field of soft magnetic material (Sun et al., 1997) and biological activities, such as the effective inhibition of DNA synthesis in tumor cells (Waring, 1981;Fisher et al., 1985). As part of a serial structural investigation of metal complexes with DABT (Liu et al., 2003), while preparing the Mn II complex of DABT, the title H 2 DABT 2+ salt was unexpectedly obtained, and its X-ray structure is presented here.
The structure of the title salt is shown in Fig. 1. The diprotonated DABT dication, H 2 DABT, is located on an inversion center while the 3-nitrobenzoate anion is placed in general position. The H 2 DABT moiety displays a trans planar configuration, which agrees with that found in the neutral DABT (Liu et al., 2003). The C-N(amino) bond length of 1.333 (4) Å is similar to the C-N(thiazole ring) bond length, 1.316 (4) Å, indicating electron delocalization between the amino and thiazole groups. It is notable that the protonated N atoms form hydrogen bonds to O atoms of carboxylate groups of 3-nitrobenzoate anions, to form supramolecular chains. This feature is consistent with those found in the H 2 DABT salt formed with 2-nitrobenzoate, which we reported previously (Liu et al., 2005).
The carboxylate group of 3-nitrobenzoate anion is twisted with respect to the benzene plane, with a dihedral angle of 13.6 (4)°, which is comparable with 13.1 (2)° found in the 2-nitrobenzoate H 2 DABT salt (Liu et al., 2005). This distortion allows the formation of the observed supramolecular structure (Fig. 2).

Refinement
H atoms bonded to C atoms were placed in calculated positions with C-H = 0.93 Å, and included in the final cycles of refinement in riding mode, with U iso (H) = 1.2U eq (carrier C). H atoms bonded to N atoms were located in a difference map and refined as riding in their as found relative positions, with U iso (H) = 1.2U eq (carrier N).
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title salt, with 30% probability displacement ellipsoids (arbitrary spheres for H atoms), dashed lines showing the hydrogen bonding within the complex [symmetry code: (i) 2 - x,1 -y,1 -z].