Crystal structure and Hirshfeld surface analysis of (succinato-κO)[N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine-κ5 O,N,N′,O′,O′′]nickel(II) tetrahydrate

One O atom of the succinate anion and three O atoms and two N atoms from a tetrakis(2-hydroxyethyl)ethylenediamine ligand coordinate to the NiII cation to form the complex which has a distorted octahedral geometry.

Crystal structure and Hirshfeld surface analysis of (succinato-jO) [N,N,N  In the title compound, [Ni(C 10 H 24 N 2 O 4 )(C 4 H 4 O 4 )]Á4H 2 O, the Ni II cation is octahedrally coordinated by one O atom of the succinate anion and three O atoms and two N atoms from an N,N,N 0 ,N 0 -tetrakis(2-hydroxyethyl)ethylenediamine molecule. In the crystal, molecules are linked by O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional supramolecular architecture. Hirshfeld surface analyses and two-dimensional fingerprint plots were used to analyse the intermolecular interactions present in the crystal, indicating that the most important contributions for the crystal packing are from HÁ Á ÁH (63.3%) and HÁ Á ÁO/OÁ Á ÁH (34.5%) interactions.

Chemical context
Aliphatic dicarboxylic acid ligands have been utilized consistently in the synthesis of a diverse range of metal complexes. The metal-ion geometries of coordination compounds can easily be identified. Transition metal atoms can be bridged by aliphatic or aromatic dicarboxylate ligands to produce chains, layers and frameworks (Pavlishchuk et al., 2011;Cheng et al., 2013;Ş en et al., 2017). In addition, 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 as a result of their antiepileptic, antimicrobial, antibacterial and anticancer activities (Bombicz et al., 2001). Nickel complexes with succinic acid [chemical formula (CH 2 ) 2 (CO 2 H) 2 ] are examples containing a dicarboxylic acid. The carboxyl O atoms ligate to transition metals and thus the succinic acid can bridge between nickel metal centres to form one-, two-and threedimensional structures as polymeric chains, layers and frameworks, respectively. We describe herein the synthesis and structural features of a new Ni II complex,N,N 0 ,N 0 -tetrakis(2-hydroxyethyl)ethylenediamine-5 O,N,N 0 ,O 0 ,O 00 ]nickel(II) tetrahydrate. In addition, to understand the intermolecular interactions in the crystal structure, Hirshfeld surface analysis was performed.

Figure 1
The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 20% probability level.

Figure 2
A view of the crystal packing of the title compound along the c axis.

Hirshfeld surface analysis
Hirshfeld surface analysis was used to investigate the presence of hydrogen bonds and intermolecular interactions in the crystal structure and two-dimensional fingerprint plots were calculated using CrystalExplorer (Turner et al., 2017). The molecular Hirshfeld surfaces were performed using a standard (high) surface resolution with the three-dimensional d norm surfaces mapped over a fixed colour scale of À0.7407 (red) to 1.6068 (blue) a.u. The red spots on the surface indicate the intermolecular contacts involved in the hydrogen bonds. The red spots identified in Figs. 3 and 4 correspond to the near-type HÁ Á ÁO contacts resulting from O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (Table 2). Fig. 5 shows the two-dimensional fingerprint plot for the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. The graph shown in Fig. 6 represents the OÁ Á ÁH/HÁ Á ÁO contacts (34.5%) between the oxygen atoms inside the surface and the hydrogen atoms outside the surface, d e + d i = 1.7 Å , and has two symmetrical points at the top, bottom left and right. These data are characteristic of O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds ( Table 2). The top plot shown in Fig. 6 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 = 1.0 Å , which indicates the presence of the HÁ Á ÁH contacts (63.3% contribution). The graph for CÁ Á ÁH/HÁ Á ÁC represents the contacts ((1.4% contribution) between the carbon atoms inside the Hirshfeld surface and the hydrogen atoms outside it and vice versa. It has two symmetrical wings on the left and right sides.
In the view of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.308 to 0.257 a.u. using the STO-3G basis set at the Hartree-Fock level of theory, Fig. 7, the C-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bond donors and acceptors are shown as blue and red areas around the atoms with positive (hydrogenbond donors) and negative (hydrogen-bond acceptors) electrostatic potentials, respectively.

Synthesis and crystallization
A solution of NaOH (50 mmol, 2.0 g) was added to an aqueous solution of succinic acid (25 mmol, 3 g) under stirring. A solution of NiCl 2 Á6H 2 O (25 mmol, 6.14 g) in methanol was added. The mixture was heated at 353 K for one h and then the blue mixture was filtered and left to dry at room temperature. The product ( The Hirshfeld surfaces of the title compound mapped over d norm , d i and d e .

Figure 4
Hirshfeld surface mapped over d norm to visualize the intermolecular interactions.

Figure 5
The fingerprint plot for all interactions. kis(2-hydroxyethyl)ethylenediamine (1.75 mmol, 0.41 g). The mixture was heated at 353 K for one h under stirring and the resulting suspension was filtered. It was allowed to crystallize for four weeks at room temperature. Blue prismatic crystals suitable for X-ray diffraction analysis were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. C-bound H atoms were geometrically positioned with C-H distances of 0.93-0.97 Å . and refined as riding, with U iso (H) = 1.2U eq (C). N-bound H atoms were located in difference-Fourier maps and refined isotropically. The water H atoms were located in a difference map and were refined subject to a DFIX restraint of O-H = 0.85 Å . The O12-H12C bond length was refined with a DFIX restraint of 0.84 (4) Å . The H atoms bonded to other O atoms (O5, O6, O7 and O8) were located in a difference map and refined freely.

Figure 7
Hirshfeld surface plotted over electrostatic potential energy.

sup-1
Acta Cryst. SHELXL2018 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009). 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.