catena-Poly[lead(II)-bis(μ-2-amino-1,3-benzothiazole-6-carboxylato)]

The title complex, [Pb(C8H5N2O2S)2]n, consists of one PbII ion located on a crystallographic twofold axis and two symmetry-related 2-amino-1,3-benzothiazole-6-carboxylate (ABTC) ligands. The central PbII ion has a (4 + 2) coordination by four O atoms of the two ABTC ligands and two weaker Pb—S bonding interactions (Pb—S secondary bonds) from S atoms of other two neighbouring ABTC ligands. These bonds link the metal ions into zigzag chains along the c axis, which, in turn, aggregate through π–π interactions [centroid–centroid distance = 3.7436 Å] between ABTC rings and N—H⋯O and N—H⋯N hydrogen bonds.


Comment
In recent years, benzothiazole and its derivatives have been attracting more attention because they exhibit interesting optical and biological activities, which made them widely used in many fields, such as fluorescent materials, nonlinear optical materials, pesticides, anti-tumor and anti-microbial drugs, etc. (Petkova et al., 2000;Leng et al., 2001;Karlsson et al., 2003;Ćaleta et al., 2009). Related structural studies are partly focused on the fact that the benzothiazole ring contains N, S and O as potential donor atoms, which exhibit good coordination capacity, and so are propitious to build novel complexes (Zou et al.,2004;Vuoti et al., 2007;Ng et al., 2008;Chen et al.,2010;). By reviewing their metal complexes (Cambridge Structural Datebase, Version of 5.31 of August 2010; Allen, 2002), it was found that most metal atoms only match with N atom of thiazole ring, but not the S atom (because the coordination capacity of S is much weaker than N), as long as these metal atoms have interaction with the thiazole ring. In our recent work, accompanied with the design and synthesis of benzothiazole derivatives Fang et al., 2010), complexes of benzothiazole derivatives with metal atoms were composed and structurally analyzed to explore their coordination behaviors. In this paper, we report the structure of a coordination polymer of lead and 2-amino-1,3-benzothiazole-6-carboxylate ligand (ABTC), where the coordination mode of S with Pb is seen as a secondary Pb-S bond (Chan et al., 1997;Turner et al., 2008).
In the crystal, two S atoms also interacte with the apical Pb II ion with so-called secondary bonds, where the Pb-S distance [Pb1-S1 i ( (i) x, -y, z+1/2) and Pb1-S1 ii , with a distance of 3.3894 (17) Å] is shorter than the corresponding sum of the van der Waals radii (3.80 Å) of Pb and S atoms (Bondi, 1964). So the Pb II ion in this structure should be described as (4 + 2) coordinated (Chan et al.,1997;Calatayud et al.,2007;Turner et al., 2008;Pena-Hueso et al., 2008). Under this coordination mode, each ABTC ligand acts as a linear linker to coordinate two metal centers, while each metal ion is linked to four ABTC ligands, then, along the c axis, one-dimensional zigzag chains are formed (Figure 2).
Along the b axis, neighboring chains are linked by N-H···O H-bonds and π-π interactions between the thiazole and benzene rings [with perpendicular distance of 3.4184Å and centroid-centroid distance of 3.7436 Å]. Simultaneously, there is an interaction between the benzene ring and the carboxyl group coordinated on the Pb II ion, described by the 4-membered ring supplementary materials sup-2 of O1-C8-O2-Pb1, with a perpendicular distance of 3.5021Å and centroid-centroid distance of 3.5740 Å (Sredojević et al.,2010).
Finally, along the a axis, neighboring chains are further connected to each other by N-H··· N hydrogen bonds which complete an infinite three-dimensional framework of the structure (Table 1 and Figure 3).
It is worth noting that S secondary bonds were also present in the previously reported complex of Ag and a benzothiazole derivative (Zou et al., 2004) through the weak interaction between Ag and the S atom of the thiozole ring. Also here these secondary Ag-S bonds play an important role in building the crystal framework, cooperating with the hydrogen bonds and π-π interactions to build the supramolecular structure.
Brown crystals suitable for X-ray diffraction analysis were obtained.

Refinement
All H atoms bound to C and N atoms were located in difference Fourier syntheses and were refined as riding, with C-H distances of 0.93 Å and and N-H distances of 0.86 Å . All U iso (H) were kept at 1.2U eq (Host). Fig. 1. The crystal structure of (I),drawn with 40% probability displacement ellipsoids. H atoms have been omitted for clarify. Symmetry codes: (i) 1 -x, -y,1 -z; (ii)x,-y,1/2 + z; (iii)1x, y, 3/2 -z.