Synthesis, crystal structure and Hirshfeld surface analysis of tetraaquabis(isonicotinamide-κN 1)cobalt(II) succinate

In the title CoII complex, both the cation and succinate anion are located about individual inversion centres. In the crystal, the ions are linked via O—H⋯O and N—H⋯O hydrogen bonds, forming a three-dimensional framework.


Chemical context
Metal carboxylates have attracted intense attention because of their interesting framework topologies. Among metal carboxylates, succinate dianions (succ) have good conformational freedom and they possess some desirable features such as being a versatile ligand because of the four electron-donor oxygen atoms they carry, and their ability to link inorganic moieties. Metal succinates are one of the best dicarboxylatebased moieties that display an interesting structural variety. Dicarboxylic acids such as succinic acid and amides have been particularly useful in creating many supramolecular structures between isonicotinamide and a variety of carboxylic acid molecules (Vishweshwar et al., 2003;Aakerö y et al., 2002). Dicarboxylic acid ligands have been utilized frequently in the synthesis of various metal carboxylates. For this reason they have been investigated widely, both experimentally and computationally. We describe herein the synthesis, structural features and Hirshfeld surface analysis of a new tetraaquabis(isonicotinamide-N 1 )cobalt(II) succinate complex.

Structural commentary
The molecular structure of the title complex is illustrated in Fig. 1. The cobalt(II) ion is coordinated octahedrally by four O atoms of water molecules and two N pyridine atoms of isonicotinamide molecules. The values of the Co-O water and Co-N pyridine bond lengths and the bond angles involving atom Co1 (Table 1)

Supramolecular features
In the crystal, the chains formed by O-HÁ Á ÁO hydrogen bonds involving the succinate anions and the complex cations are linked by further O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional supramolecular architecture (Table 2 and Fig. 2). Within the framework, C-HÁ Á ÁO hydrogen bonds are also present (Table 2).

Hirshfeld surface analysis
CrystalExplorer17.5 (Turner et al., 2017) was used to analyse the interactions in the crystal. The molecular Hirshfeld surfaces were obtained using a standard (high) surface resolution with the three-dimensional d norm surfaces mapped over a fixed colour scale of À0.728 (red) to 1.428 (blue). The red spots in the d norm surface (Fig. 3), indicate the regions of donor-acceptor interactions given in Table 2.
The view of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.366 to 0.236 a.u. using the STO-3G basis set at the Hartree-Fock level of theory is given in Fig. 4. The C-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bond donors and acceptors are shown as blue and red areas around the related research communications Figure 1 The molecular structure of the title complex, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
A view along the b axis of the crystal packing of the title complex. Dashed lines indicate the hydrogen bonds (see Table 2). atoms with positive (hydrogen-bond donors) and negative (hydrogen-bond acceptors) electrostatic potentials, respectively.
The fingerprint plot for the title complex is presented in Fig. 5. The contribution from the OÁ Á ÁH/HÁ Á ÁO contacts, corresponding to C-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁO interactions, is represented by a pair of sharp spikes characteristic of a strong hydrogen-bonding interaction (43%) (Fig. 6a). The HÁ Á ÁH interactions appear in the middle of the scattered points in the two-dimensional fingerprint plots with an overall Hirshfeld surface of 39.8% (Fig. 6b). The contribution of the other intermolecular contacts to the Hirshfeld surfaces is CÁ Á ÁH/HÁ Á ÁC (8.4%) (Fig. 6c). The CÁ Á ÁC/CÁ Á ÁC contacts with 3.8% contribution appear as points of low density (Fig. 6d).

Synthesis and crystallization
An aqueous solution of succinic acid (25 mmol, 3 g) was added to a solution of NaOH (50 mmol, 2 g) under stirring. An aqueous solution of CoCl 2 Á6H 2 O (25 mmol, 5.95 g) was added and the reaction mixture stirred for 30 min at room temperature. The pink mixture obtained was filtered and left to dry. The pink crystalline material ( The fingerprint plot of the title compound.   A view of the three-dimensional Hirshfeld surface of the title complex, plotted over the electrostatic potential energy. obtained was dissolved in water and added to a aqueous solution of isonicotinamide (1.71 mmol, 0.21 g). The resulting suspension was filtered and the filtrate allowed to stand. Red prismatic crystals were obtained from the filtrate in five weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The water and NH 2 H atoms were located from difference-Fourier maps and freely refined. The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C).

Tetraaquabis(isonicotinamide-κN 1 )cobalt(II) butanedioate
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.

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