Crystal structure and Hirshfeld surface analysis of tetraaquabis(isonicotinamide-κN 1)nickel(II) fumarate

In the crystal, the NiII complex cation and fumarate anion are located on individual inverse centers and linked via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds.


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 the biological processes involved in the formation of vitamins and drug components. An important element for biological systems is nickel and nickel complexes have biological activities including antiepileptic, antimicrobial, antibacterial and anticancer activities (Bombicz et al., 2001). Dicarboxylic acid ligands have been utilized primarily in the synthesis of a range of metal complexes. Dicarboxylic acids such as fumaric acid and amides have been particularly useful in creating many supramolecular structures (Pavlishchuk et al., 2011;Ostrowska et al., 2016), in particular isonicotinamide with a variety of carboxylic acids (Vishweshwar et al., 2003;Aakerö y et al., 2002).
We have prepared a new Ni II complex, tetraaquabis-(isonicotinamide-N 1 )nickel(II) fumarate, and determined its structure by single crystal X-ray diffraction. In addition, Hirshfeld surface analysis and fingerprint plots were used to ISSN 2056-9890 understand the intermolecular interactions in the crystal structure.

Structural commentary
The molecular structure of the title complex is illustrated in Fig. 1. The nickel(II) ion is octahedrally coordinated to four water O atoms and two N pyridine atoms of isonicotinamide molecules. The values of the Ni-O water and Ni-N pyridine bond lengths and the bond angles involving atom Ni1 (Table 1) are close to those reported for similar nickel(II) complexes (Krä mer et al., 2002;Bora & Das, 2011;Moroz et al., 2012).

Figure 2
A view of the crystal packing of the title compound. Dashed lines indicate hydrogen bonds.

Figure 1
The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 20% probability level.
Symmetry codes: (iii) Àx þ 2; y À 1 2 ; Àz þ 1 2 ; (iv) Àx þ 1; y À 1 2 ; Àz þ 1 (high) resolution with the three-dimensional d norm surfaces mapped over a fixed colour scale of À0.701 (red) to 1.286 (blue) a.u. The red spots in Fig. 4 correspond to the near-type HÁ Á ÁO contacts resulting from O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. Fig. 5 shows the two-dimensional fingerprint plot of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. In Fig. 6a The Hirshfeld surface of the title compound mapped over d norm , d i and d e .

Figure 4
The Hirshfeld surface mapped over d norm to visualize the intramolecular and intermolecular interactions in the title compound.

Synthesis and crystallization
A solution of NaOH (52 mmol, 2.07 g) was added to an aqueous solution of fumaric acid (26 mmol, 3 g) under stirring. A solution of NiCl 2 Á6H 2 O (25 mmol, 6.14 g) in methanol was then added. The mixture was heated at 353 K for 30 min. and then the blue mixture was filtered and left to dry at room temperature. The reaction mixture (0.88 mmol, 0.20 g) was dissolved in methanol and added to a ethanol solution of isonicotinamide (1.76 mmol, 0.21 g). The mixture was heated at 353 K for 60 min. under stirring and the resulting suspension was filtered and left to crystallize for three weeks at room temperature. The title compound was obtained as a blue solid and contained crystals suitable for X-ray diffraction analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The water and NH 2 hydrogen 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).  SHELXL2017 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

Tetraaquabis(isonicotinamide-κN 1 )nickel(II) fumarate
Crystal data [Ni(C 6  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. Refinement. Refined as a 2-component inversion twin.