Bis(4,4′-bipyridyl)bis{2-[4,6-bis(carboxymethylsulfanyl)-1,3,5-triazin-2-ylsulfanyl]acetato}zinc(II)

In the title compound, [Zn(C9H8N3O6S3)2(C10H8N2)2], the central ZnII ion, situated on a center of inversion, adopts an octahedral geometry coordinated by four O atoms from two carboxylate groups and two carboxylic groups of two symmetry-related TTTA ligands and two N atoms from two bpy molecules {TTTA is 2,2′,2′′-[1,3,5-triazine-2,4,6-triyltris(sulfanediyl)]triacetic acid and bpy is 4,4′-bipyridine}. These mononuclear units are connected through complementary O—H⋯X hydrogen bonds, as well as through weak C—H⋯X (X = O and N) interactions, resulting in a three-dimensional supramolecular architecture.

We acknowledge the National Natural Science Foundation of China (grant No. 20801025 and 20671048) for financial support.

Comment
Recent years have witnessed rapid development of the construction of metal-organic assemblies with fascinating structures and properties in coordination chemistry and crystal engineering. (Moulton & Zaworotko, 2001;Rao et al., 2004;Ferey et al., 2005). Besides metal-ligand coordination bonding, various kinds of intermolecular weak interactions, such as hydrogen bonds, weak C-H···X (X = O, N, π) interactions and π···π stacking, are also vital in the self-assembly process. (Braga & Grepioni, 2000;Roesky & Andruh, 2003;Chen et al., 2009) Our interest is the coordination chemistry of semirigid polycarboxylate ligands by introducing functional groups between the aromatic ring and carboxylate groups (Hong et al., 2005;Wang et al., 2007;Sun et al., 2007).
Herein we report the title compound [Zn(TTTA) 2 (bpy) 2 ] (TTTA = 2,2',2''-[1,3,5-triazine-2,4,6-triyltris(thio)]tris-acetic acid, bpy = 4,4'-bipyridine), as illustrated in Scheme 1 and Figure 1. The Zn II ion, situated on a center of inversion, adopts octahedral geometry with four oxygen atoms from two carboxylate groups and two carboxylic groups of two different TTTA ligands and two nitrogen atoms from two coordinated bpy molecules. Only one carboxylate group of the TTTA ligand is deprotonated and coordinated to the metal center in a monodentate mode. The atoms in the central triazine ring are almost coplanar with a very small deviation of only 0.0085 Å from the mean plane and the dihedral angle of the carboxylate group with the triazine ring is 75.6 (2)°. The other two -COOH groups, one of which is coordinated and the other uncoordinated, form the dihedral angles of 80.0 (2) and 175.0 (4)° with the triazine ring, respectively.
As shown in Figure 2, significant O-H···N hydrogen bonding interactions are generated between hydroxyl groups (O5-H5) of the carboxylic acid and uncoordinated nitrogen atom (N5) from adjacent molecules. As a result, one-dimensional hinged chains containing M 2 L 2 (bpy) 2 macrocyclic rings are formed along the b axis. These chains are further linked together in a parallel fashion to form a two-dimensional sheet through O-H···O hydrogen bonds between the carboxylate group (O2) and carboxyl oxygen atom (O4) from adjacent chains. Between neighboring sheets, bpy (C13 and C18) CH groups form weak C-H···O weak interactions with TTTA carboxyl oxygen atoms (O6). Simultaneously, these sheets are consolidated further through weak C-H···N interactions between CH 2 groups (C6) and N atoms (N1) of the triazine ring ( Figure 3 and   Fig. 1. The local coordination environment for the Zn II centers in 1. Hydrogen atoms have been omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level. Selected bonds information is listed in Table 1. Symmetry codes: (i) 1-x, -y, 1-z.  Crystal data [Zn(C 9

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.