Crystal structure of poly[[aqua(μ-2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-dicarboxylato-κ2 O 5:O 7)[μ-di(pyridin-4-yl)sulfane-κ2 N:N′]zinc] 0.26-hydrate]

The zinc cation in the structure has a N2O3 coordination set, arranged in a trigonal–bipyramidal configuration. The bridging mode of the organic ligands leads to the formation of a polymeric layer structure parallel to the ab plane.


Chemical context
Complexes constructed by metal ions and organic ligands are of continuous interest due to the vast diversity and feasible tailorability of their structures and functions compared with purely inorganic compounds (Zhang et al., 2015).
The incorporation of both carboxylic and pyridine ligands can lead to a variety of structures (Schoedel et al., 2016). Complexes based on thiophene derivatives with carboxylic acid functionalities are of some interest as anticancer agents (Chen et al., 1998(Chen et al., , 1999Guo et al., 2009). In this context, we report here on synthesis and crystal structure of the title compound, [Zn(C 8 H 4 O 6 S)(C 10 H 8 N 2 S)(H 2 O)]Á0.26H 2 O, (1).

Structural commentary
In the crystal structure of (1), the zinc ion is coordinated by four organic ligands and one water molecule, giving rise to a slightly distorted trigonal-bipyramidal coordination environment. Two nitrogen atoms are delivered by two symmetryrelated pyridine ligands, two oxygen atoms of two carboxyl groups stem from two symmetry-related thiophene carboxyl- ISSN 2056-9890 ate ligands, and one O atom from the aqua ligand (Fig. 1). In the trigonal bipyramid, the axial angle O7-Zn1-N2 is 171.31 (6) . The Zn II ion is co-planar with the O5-N1-O4 equatorial plane, with the deviation of the Zn atom from this plane being 0.0034 (3) Å . The equatorial Zn1-N1 bond length is 2.1131 (18) Å , while the axial Zn1-N2 bond is longer, 2.2107 (18) Å . Similarly, the two equatorial Zn1-O (O4, O5) bond lengths, ranging from 1.9835 (15) to 2.0285 (15) Å , are shorter than the axial Zn1-O7 bond of 2.1375 (17) Å . These are typical values, numerical details of which are given in Table 1.

Supramolecular features
The bridging coordinating mode of the organic ligands leads to the formation of polymeric layers parallel to the ab plane (Fig. 2).
There are several types of hydrogen bonds in the structure. One intramolecular hydrogen bond is present and extends from a (pyridine)C-H group (C10-H10A) to the coordinating O5 atom of the carboxyl group. Another (pyridine)C-H group (C18-H18A) is hydrogen-bonded to the disordered O8 atom of the lattice water molecule. Three O-HÁ Á ÁO interactions are present between the coordinating water molecule to either the carboxyl group oxygen atoms or the dioxine oxygen atom in the thiophene derivative with DÁ Á ÁA distances ranging between 2.733 (2) and 3.123 (2) Å and corresponding O-HÁ Á ÁO angles of 135 (2) and 159 (2) . Numerous other C-HÁ Á ÁO interactions are present between the disordered dioxine C-H groups and a carboxyl O atom (O6) or the lattice water atom O8. Other C-HÁ Á ÁO interactions involve pyridyl C-H groups and the carboxyl O3 atom. In addition, one C-HÁ Á ÁS interaction and one C-HÁ Á ÁN interaction are found between pyridyl C-H groups and the sulfane S1 atom or the pyridyl N1 atom (Fig. 3). It is expected that other extensive hydrogen bonds are formed with the lattice water molecules as the donor group and the coordinating water molecules or carbonyl O atoms from the layers as acceptors (O8Á Á ÁO distances in the range 2.87-3.13 Å ). However, since the H atoms of the disordered O8 atom were not modelled, a definite statement cannot be made. Numerical details of the hydrogen bonding are given in Table 2.

Figure 2
The polymeric layer in the crystal structure of (1), extending along the ab plane (H atoms have been omitted for clarity).
2015) have been reported, but a complex incorporating both ligands was not found.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms attached to carbon were positioned geometrically and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C). The H atoms of the coordinating water molecule were located in a difference map and restrained to have comparable bond lengths using DFIX and DANG commands to keep their geometries reasonable; U iso (H) values were set to 1.5U eq (O). The hydrogen atoms of the disordered lattice water molecule [occupancy 0.262 (10)] could not be retrieved from difference maps and thus were not part of the model. Two carbon atoms of the dioxine moiety are disordered over two sets of sites and were refined in two parts (C3-C4/C3A-C4A) with a refined occupancy ratio of 0.624 (9)/0.376 (9). Soft restraints (DFIX, SIMU, SADI) were applied on the disordered atoms to keep their geometries and atomic displacement parameters reasonable.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (