Crystal structure and Hirshfeld surface analysis of aquabis(nicotinamide-κN)bis(4-sulfamoylbenzoato-κO 1)copper(II)

The CuII cation, located on a twofold rotation axis, is coordinated by two 4-sulfamoylbenzoate anions, two nicotinamide (NA) molecules and one water molecule in a slightly distorted square-pyramidal geometry.

In the crystal of the title complex, [Cu(C 7 H 6 NO 4 S) 2 (C 6 H 6 N 2 O) 2 (H 2 O)], the Cu II cation and the O atom of the coordinated water molecule reside on a twofold rotation axis. The Cu II ion is coordinated by two carboxylate O atoms of the two symmetry-related 4-sulfamoylbenzoate (SB) anions and by two N atoms of the two symmetry-related nicotinamide (NA) molecules at distances of 1.978 (2) and 2.025 (3) Å , respectively, forming a slightly distorted square-planar arrangement. The distorted square-pyramidal coordination environment is completed by the water O atom in the axial position at a distance of 2.147 (4) Å . In the crystal, the molecules are linked via O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds with R 2 2 (8) and R 2 2 (18) ring motifs, forming a three-dimensional architecture. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from HÁ Á ÁO/ OÁ Á ÁH (42.2%), HÁ Á ÁH (25.7%) and HÁ Á ÁC/CÁ Á ÁH (20.0%) interactions.

Chemical context
Nicotinamide (NA) is one form of niacin. A deficiency of this vitamin leads to loss of copper from the body, known as pellagra disease. Victims of pellagra show unusually high serum and urinary copper levels (Krishnamachari, 1974). The NA ring is the reactive part of nicotinamide adenine dinucleotide (NAD) and its phosphate (NADP), which are the major electron carriers in many biological oxidation-reduction reactions (You et al., 1978). The nicotinic acid derivative N,N-diethylnicotinamide (DENA) is an important respiratory stimulant (Bigoli et al., 1972).
Transition metal complexes with ligands of biochemical interest such as imidazole and some N-protected amino acids show interesting physical and/or chemical properties, through which they may find applications in biological systems (Antolini et al., 1982). The crystal structures of metal complexes with benzoic acid derivatives have been reported extensively because of the varieties of the coordination modes, for example, Co and Cd complexes with 4-aminobenzoic acid (Chen & Chen, 2002). The structures of some mononuclear complexes obtained from the reactions of transition metal(II) ions with nicotinamide (NA) and some benzoic acid derivatives as ligands have been determined previously, e.g.
[Zn (C 7  The structure determination of the title compound, (I), a copper complex with two 4-sulfamoylbenzoate (SB) anions and two nicotinamide (NA) ligands and one coordinated water molecule, was undertaken in order to compare the results obtained with those reported previously. In this context, we synthesized the Cu II -containing title compound, aquabis(nicotinamide-N)bis(4-sulfamoylbenzoato-O 1 )copper(II), [Cu(C 7 H 6 NO 4 S) 2 (C 6 H 6 N 2 O) 2 (H 2 O)], and report herein its crystal and molecular structures along with the Hirshfeld surface analysis.

Structural commentary
The asymmetric unit of the crystal structure of the mononuclear title complex, (I), contains one half of the Cu II ion, one 4-sulfamoylbenzoate (SB) anion and one nicotinamide (NA) molecule together with one half water molecule, all ligands coordinating in a monodentate manner (Fig. 1).

Figure 2
Part of the crystal structure, viewed down the b axis. O-H W Á Á ÁO C , N-H NA Á Á ÁO NA , N-H SB Á Á ÁO C and N-H SB Á Á ÁO SB (W = water, C = carboxylate, NA = nicotinamide and SB = 4-sulfamoylbenzoate) hydrogen bonds, enclosing R 2 2 (8) and R 2 2 (18) ring motifs, are shown as dashed lines. H atoms not involved in these interactions have been omitted for clarity. benzoate ions are coordinated to the metal atoms only monodentately in (III) and (IV), and both monodentately and bidentately in (II). In the SB anion, the carboxylate group is twisted away from the attached C2-C7 benzene ring by 20.92 (17) , while the benzene and N1/C8-C12 pyridine rings are oriented at a dihedral angle of 81.86 (12) .
Hydrogen bonding and van der Waals contacts are the dominant interactions in the crystal packing. No significant -, C-HÁ Á Á or C-HÁ Á ÁO interactions are observed.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title complex, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using Crystal Explorer 17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 3) View of the three-dimensional Hirshfeld surface of the title complex plotted over d norm in the range À0.7548 to 1.5398 a.u.

Figure 4
View of the three-dimensional Hirshfeld surface of the title complex plotted over electrostatic potential energy in the range À0.1045 to 0.2914 a.u. using the STO-3G basis set at the Hartree-Fock level of theory. N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bond donors and acceptors are shown as blue and red regions around the atoms corresponding to positive and negative potentials, respectively. contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The brightred spots appearing near SB-O1, SB-O4, NA-O5 and hydrogen atoms H21, H31, H32 and H61 indicate their role as the respective donors and acceptors in the dominant O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds; they also appear as blue and red regions, respectively, corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005) as shown in Fig. 4 (Fig. 5c), the 25.7% contribution to the overall crystal packing is reflected as widely scattered points of high density due to the large hydrogen content of the molecule. In the absence of C-HÁ Á Á interactions in the crystal, the pair of characteristic wings resulting in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts with a 20.0% contribution to the HS, Fig. 5d, and the pair of edges at d e + d i $2.58 Å result from short interatomic HÁ Á ÁC/CÁ Á ÁH contacts. The HÁ Á ÁN/NÁ Á ÁH (Fig. 5e) and OÁ Á ÁC/CÁ Á ÁO (Fig. 5f) Fig. 6a-e, respectively. The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The large number of HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁH and HÁ Á ÁC/CÁ Á ÁH interactions suggest that van der Waals interactions and hydrogen bonding play the major roles in the crystal packing (Hathwar et al., 2015).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms of the water molecule and the NH 2 group of the nicotinamide (NA) molecule were located in a difference-Fourier map and refined freely. H atoms of the NH 2 group of the 4-sulfomylbenzoate (SB) group were also located in a difference-Fourier map and the positions were refined with U iso (H) = 1.5U eq (N). The aromatic Cbound H atoms were positioned geometrically with C-H = 0.93 Å , and refined as riding with U iso (H) = 1.2U eq (C).

Aquabis(nicotinamide-κN)bis(4-sulfamoylbenzoato-κO 1 )copper(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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.