Synthesis, crystal structure and Hirshfeld surface analysis of a 1D coordination polymer catena-poly[[diaquabis(nicotinamide-κN 1)nickel(II)]-μ-fumarato-κ2 O 1:O 4]

In the crystal, the fumarate dianions bridge the NiII cations into polymeric chains propagating along the [101] direction; these polymeric chains are further linked by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional supramolecular architecture.


Chemical context
Metal complexes of biologically important ligands are sometimes more effective than the free ligands. Many transition and heavy metal cations play an important role in biological processes in the formation of many vitamins and drug components. An important element for biological systems is nickel. Nickel complexes have biological applications such as antiepileptic, antimicrobial, antibacterial and anticancer activities (Bombicz et al., 2001). The metal-ion geometries of coordination compounds can be easily identified. Dicarboxylic acid ligands are utilized in the synthesis of a range of metal complexes and fumaric acid and amide have been particularly useful in creating many supramolecular structures (Pavlishchuk et al., 2011;Ostrowska et al., 2016), in particular between nicotinamide and a variety of carboxylic acid molecules. We have prepared a new Ni II complex, catena-poly[[diaquabis-(nicotinamide-N 1 )nickel(II)]--fumarato-2 O 1 :O 4 ], whose structure has been determined by single crystal X-ray diffraction analysis. In addition, to understand the intermolecular interactions in the crystal structure, Hirshfeld surface analysis was performed.

Structural commentary
The molecular structure of the asymmetric unit of the title compound is illustrated in Fig. 1. This linear one-dimensional coordination polymer consists of a nickel centre coordinated ISSN 2056-9890 in an octahedral fashion by two oxygen atoms of fumaric acid dianions, two nicotinamide nitrogen atoms and two aqua ligands.

Figure 2
A partial view of the crystal packing of the title compound. Dashed lines indicate the hydrogen bonds (see Table 1).
mapped over a fixed colour scale of À1.219 (red) to 1.466 (blue) a.u. Fig. 5 shows the two-dimensional fingerprint of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. The graph shown in Fig. 6a represents the OÁ Á ÁH/HÁ Á ÁO contacts (35.9%) between the oxygen atoms inside the surface and the hydrogen atoms outside the surface, d e + d i = 1.9 Å , and two symmetrical points at the top, bottom left and right. These are characteristic of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. Fig. 6b (HÁ Á ÁH) shows the twodimensional fingerprint of the (d i , d e ) points associated with hydrogen atoms. It is characterized by an end point that points to the origin and corresponds to d i = d e = 1.08 Å , which indicates the presence of the HÁ Á ÁH contacts in this study (31.7%). The graph shown in Fig. 6d (CÁ Á ÁH/HÁ Á ÁC) shows the contact between the carbon atoms inside the surface and the hydrogen atoms outside the Hirshfeld surface and vice versa (9.5%). In addition, CÁ Á ÁC (10.4%), NÁ Á ÁH/HÁ Á ÁN (3.6%) and NiÁ Á ÁO/OÁ Á ÁNi (3.4%) contacts contribue to the Hirshfeld surface.

Synthesis and crystallization
A solution of NaOH (52 mmol, 2.07 g) was added to an aqueous solution of H 2 Fum (26 mmol, 3 g) with stirring. A solution of NiCl 2 Á6H 2 O (26 mmol, 6.14 g) in ethanol was added. The mixture was heated at 353 K for an hour and then the pink mixture was filtered and left to dry at room temperature. The reaction mixture (0.88 mmol, 0.20 g) was   The Hirshfeld surface of the title compound mapped over d norm , d i and d e .

Figure 4
Hirshfeld surfaces mapped over d norm to visualize the intermolecular interactions of the title compound.

Figure 5
A fingerprint plot of the title compound. dissolved in ethanol and added to a methanol solution of nicotinamide (1.76 mmol, 0.21 g). The mixture was heated at 353 K for 30 min with stirring and the resulting suspension was filtered. On slow evaporation of the filtrate, over a period of three weeks, blue block-shaped crystals of the title complex were obtained.

catena-poly[[diaquabis(nicotinamide-κN 1 )nickel(II)]-µ-fumarato-κ 2 O 1 :O 4 ]
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.