Crystal structure of poly[{μ3-(E)-3-[3-(carboxylatomethoxy)phenyl]acrylato-κ3 O,O′:O′′:O′′′}[μ2-3-(pyridin-4-yl)-1H-pyrazole-κ2 N:N′]cobalt(II)]

A two-dimensional polymeric structure based on (E)-3-(3-(carboxymethoxy)phenyl)acrylic acid (H2 L) and 3-(pyridin-4-yl)pyrazole (pp) ligands, has been successfully synthesized under solvothermal conditions. In the crystal, helical chains formed by pp and L ligands connected to the Co metal, propagate parallel to the a axis.


Chemical context
The rational design and synthesis of metal-organic frameworks (MOFs) with multi-carboxylate ligands and metal atoms has attracted much attention in coordination chemistry due to the varied topologies and potential applications in catalysis, gas adsorption, photochemistry etc (Ferná ndez et al., 2016). The versatility of metal-organic chemistry offers the opportunity to construct multifunctional materials based on the assembly of molecular building blocks. Much attention has been devoted to the cogitative design and control of selfassembly of infinite coordination networks by careful selection of ligand geometry (Liu et al., 2016;Yoon et al., 2012). In this regard, the use of symmetrical ligands has been a successful paradigm because of their structural predictability (Rosi et al., 2003;Luo et al., 2003). Incorporation of unsymmetrical ligands in such systems, however, is relatively recent (Wang et al., 2004;Chen et al., 2003;Qin et al., 2005). Compared to symmetrical ligands, ligands with two or more coordination sites with differing donor ability can lead to unsymmetrical ligands being assembled around metal atoms in diverse arrangements. This can result in unprecedented structures with novel topological features, such as a clay-like double layer (Pan et al., 2000), large spherical cavities and functional 1D channels (Shin et al., 2003). Although important progress has been made in the construction of coordination polymers by applying a single type of organic ligand, research involving a combination of more than one ligand is an especially attractive target, as it allows the construction of an almost infinite number of frameworks with different crystal structures.
In our work, we use (E)-3-[3-(carboxymethoxy)phenyl]acrylic acid (H 2 L) and 3-(pyridin-4-yl)pyrazole (pp) as ligands to construct novel MOFs that are based on the following considerations: (1) the carboxylate group is conjugated with the benzene ring through a C C double bond, which makes the electron density delocalized in the ligand so that it may become more rigid when coordinating to metal ions, and have more coordination modes and conformation changes (Kong et al., 2013;Liu et al., 2010); (2) the presence of a phenolic hydroxyl group and benzene ring in the ligand allows the possibility of hydrogen bonding andstacking interactions in the crystal lattices; (3) the N-donor ligand could enhance structural stability.
We herein report the synthesis and crystal structure of [Co(C 11 H 8 O 5 )(C 8 H 7 N 3 )] n based on these two mixed ligands.

Structural commentary
As shown in Fig. 1, the asymmetric unit of the title compound comprises one Co 2+ cation, one fully deprotonated L 2À anion, and one pp ligand. The Co II atom has a distorted octahedral geometry, coordinated by four O atoms from three L 2À ligands, with Co II -O distances of 2.037 (2)-2.252 (2) Å , and two N atoms from two pp ligands with Co II -N distances of 2.130 (2) and 2.158 (3) Å . The L 2À ligand adopts two different coordination modes. In this structure, the dihedral angles between the rings in the pp ligands is 23.1 (2) . The 1D helical chains (Fig. 2) are assembled by Co 2+ cations, pp ligands and L ligands. Helical chains along the c axis are connected to adjacent chains by L ligands that bridge the Co II atoms, forming a two-dimensional polymeric structure in the ac plane (Fig. 3).
In the structure, every 3 -(E)-3-[3-(carboxymethoxy)phenyl]acrylic acid ligand is connected to three Co atoms, while every 3 -3-(pyridin-4-yl)pyrazole is connected to two Co atoms. The Co II atom connects three L 2À ligands and two pp ligands, and so can be described as a five-connected node. Thus, the topology of the structure could be given simply as a (2,3,5)-connected network. The coordination environment of the Co 2+ ion in the title complex (omitting all H atoms), showing the atom-numbering scheme for non-H atoms. Displacement ellipsoids are drawn at the 40% probability level.

Figure 2
The helical chain in the title compound (omitting all H atoms). The yellow rod indicates the direction of propagation of the helix (i.e. parallel to the c axis).

Supramolecular features
In this structure, L ligands form hydrogen bonds to the pp ligands, thereby enhancing the polymer stability (Table 1 and Fig. 3). The polymer interactions consist of N1(pyrazole)-H1AÁ Á ÁO5(x À 1 4 , Ày + 1 4 , z À 1 4 ) hydrogen bonds where each L ligand makes a hydrogen bond with a neighboring pp ligand.

Database survey
The crystal structure of a 2D polymeric Cd-containing compound with (E)-3-(3-carboxymethoxy)phenyl)acrylic acid and 1,3-di-pyridin-4-ylpropane ligands (the Cd-crystal), recently reported by Wang et al. (2014), has a similar structure to the title compound. Both structures include hydrogen bonds, though in the Cd-crystal, these are O-HÁ Á ÁO hydrogen bonds rather than N-HÁ Á ÁO as in the title compound.

Synthesis and crystallization
All of the chemical reagents and solvents are commercially available and used without further purification. Elemental analyses were carried out on a Perkin-Elmer 2400 Series II analyzer. The two-dimensional packing of the title compound. Hydrogen bonds are depicted as dashed lines. Table 1 Hydrogen-bond geometry (Å , ).
was then sealed in a 25 mL stainless steel reactor and heated to 433 K for three days. The mixture was then cooled to room temperature at a rate of 5 K h À1 , and red block-shaped crystals were obtained (yield: 62% based on Co

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms attached to carbon atoms were refined using a riding-model approximation, with U iso (H) = 1.2U eq (C) and C-H = 0.93 Å (aromatic and carbene) and 0.97 Å (methylene). Other hydrogen atoms were located in difference electron-density maps and refined freely.

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