Synthesis and crystal structure of poly[(3-amino-1,2,4-triazole)(μ3-1H-benzimidazole-5,6-dicarboxylato)cobalt(II)]

The structure of the title coordination polymer is determined by multiple hydrogen-bonding interactions. In the crystal, two ligands coordinate with the metal centre, generating chains, which are further connected with each other via N—H⋯O hydrogen bonds, and expanded into the final framework through additional N—H⋯O hydrogen bonds.


Chemical context
Over the past two decades, coordination polymers (CPs) have been demonstrated to represent a new type of crystalline organic-inorganic hybrid materials, and are unique in terms of their potentially high porosities, tunable pores, and diverse compositions (Du et al., 2013;Kitagawa et al., 2007;Cui et al., 2016). These features have enabled CPs to be constructed with great potential for various applications, such as gas adsorption/separation (Zhao et al., 2018), chemical sensing (Huang et al., 2017), heterogeneous catalysis (He et al., 2020) and energy storage/conversion (Lu et al., 2020). Meanwhile, the crystalline nature of CPs allows for the accurate determination of their structures using X-ray diffraction techniques and further, the revealing of structure-property relationships. The great potential of these compounds certainly promotes the development of synthetic strategies for new CPs. It has been demonstrated that many efficient synthetic routes, including metal exchange (Wang et al., 2017), ligand substitution (Han et al., 2014), directional construction based on secondary building units (SBUs) (Zou et al., 2016), and topology-guided reticular chemistry principles  have shown some advantages in fabricating new CPs with multiple structures and functionalities. In addition to the methods mentioned above, the mixed-ligands strategy is also considered to be an important approach for the integration of the properties of related ligands into a single coordination polymer and hence expansion of the structural diversity of CPs (Macreadie et al., 2020). In this context, we report the ISSN 2056-9890 synthesis and crystal structure of the title coordination polymer poly[(3-amino-1,2,4-triazole)( 3 -1H-benzimidazole-5,6-dicarboxylato)cobalt(II)] (1), which was prepared by the solvothermal method using two simple ligands and a cobalt salt.

Structural commentary
The title coordination polymer (1) crystallizes in the monoclinic system, P2 1 /c space group, and its asymmetric unit contains one Co 2+ center, one L 1 2À anion and one L 2 ligand (Fig. 1). The metal center adopts a typical tetrahedral linkage geometry to coordinate with two carboxylato-O atoms from two independent L 1 2À ligands and two nitrogen atoms, one from L 2 and another from an L 1 ligand. Interestingly, through the combination of two L 1 2À , two L 2 ligands and two Co 2+ ions, a basic repeating unit is constructed, resulting in the formation of a one-dimensional straight chain structure (as shown in Fig. 2). These chains are further connected via hydrogen bonding interactions (Fig. 3), generating a threedimensional framework.

Supramolecular features
As mentioned above, extensive hydrogen-bonding interactions in the crystal of the title coordination polymer are observed, the numerical values of which are presented in Table 1. As shown in Fig. 4 A view of the asymmetric unit of the title coordination polymer showing the atom numbering with displacement ellipsoids drawn at the 50% probability level.

Figure 2
A view of the one-dimensional straight chain structure within the coordination polymer.  A view of the hydrogen bonds in the title coordination polymer. Intramolecular hydrogen bonds are omitted for clarity [symmetry codes: linked by other intermolecular hydrogen bonds (e.g., N3-H3Á Á ÁO3 and N6-H6AÁ Á ÁO3), resulting in the formation of the final three-dimensional supramolecular network. Due to the regular distribution of Co 2+ metal sites, the high density of nitrogen atoms in the structure, and the packing arrangement of the supramolecular network, the coordination polymer has the potential to work as a molecular catalyst or to serve as the precursor material for preparing an electrocatalyst.

Poly[(3-amino-1,2,4-triazole)(µ 3 -1H-benzimidazole-5,6-dicarboxylato)cobalt(II)]
Crystal data 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.