Bis(3,5-dinitrobenzoato-κO)bis(ethane-1,2-diamine-κ2 N,N′)cadmium(II)

In the crystal structure, centrosymmetric molecules are linked through intermolecular N—H⋯O hydrogen bonds into sheets extending parallel to (0 1).

During systematic investigations of bioavailability and biological action enhancement of well known compounds with low bioactivity, a new mixedligand metal complex, [Cd(DNBA) 2 (en) 2 )] (DNBA = 3,5-dinitrobenzoate, C 7 H 3 N 2 O 6 ; en = ethylendiamine, C 2 H 8 N 2 ), has been synthesized. The complex molecules are located on inversion centers. Two DNBA anions monodentately coordinate the Cd II atom through an oxygen atom of the carboxylate group while two en molecules coordinate in a chelate fashion, resulting in a distorted O 2 N 4 coordination set. There is a weak intramolecular hydrogen bond of 3.099 (4) Å between the non-coordinating oxygen atom of the carboxylate group and one of the en amine groups. Three relatively weak intermolecular N-HÁ Á ÁO hydrogen bonds associate complex molecules into sheets extending parallel to (011), which are further stabilized byinteractions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from HÁ Á ÁO/OÁ Á ÁH (50.2%) and HÁ Á ÁH (21.1%) interactions.

Structure description
DNBA (= 3,5-dinitrobenzoic acid) is an organic compound that is an important corrosion inhibitor applied in photography and is used by chemists to identify alcohol components in esters and in the fluorometric analysis of creatinine (Chandrasekaran et al., 2013). DNBA demonstrates low antimicrobial activity against bacteria and yeasts with values of the half maximal inhibitory concentration (IC50) and minimum inhibition concentration (MIC) of more than 3 mmol l À1 but shows medium biological action against filamentous fungi M. gypseum with IC50 and MIC values of 2.1 and 3 mmol l À1 (microbicide effect), respectively (Vaskova et al., 2009).

data reports
En (ethylendiamine) is used in large quantities for the production of many industrial chemicals. It is a well known bidentate chelating ligand for coordination complexes (Matsushita & Taira, 1999). En itself is not biologically active against different strains of microorganisms, but its Co III complex demonstrates a strong antifungal action against a broad spectrum of Candida species (Turecka et al., 2018).
The water solubility of DNBA is low (1.35 g l À1 at 25 C; Rogers & Stovall, 2000). In order to enhance its water solubility and antimicrobial activity, we tried to apply some of the presently available approaches (Jain et al., 2015). However, more encouraging is the combination of organic salts, DNBA and en as well as mixed-ligand complexes comprising respective ligands. Promising results have already been achieved in the case of 4-nitrobenzoic acid (Ibragimov et al., 2017), 4-aminobenzoic acid (Ibragimov et al., 2016) and 3hydroxybenzoic acid (Ibragimov, 2016). A search of the Cambridge Structural Database (Groom et al., 2016) has revealed that organic salts on the basis of DNBA have already been obtained [refcodes VUJXIH (Nethaji et al., 1992) and FONCER (Jones et al., 2005)] and therefore we made another attempt and synthesized a cadmium-based mixed-ligand complex. The choice of Cd is explained by the fact that compounds based on cadmium are toxic for living organisms including fungi.
In the crystal of the title compound, the complex molecules are located on inversion centers. Two symmetry-related DNBA anions monodentately coordinate to Cd II through one of the oxygen atoms of the carboxylate group. The two en ligands coordinate in a chelate fashion through the two N atoms (Fig. 1). The bond lengths Cd-O1, Cd-N3 and Cd-N4 are 2.344 (2), 2.337 (4) and 2.322 (3) Å , respectively, and the cis-bond angles vary from 77.34 (12) to 102.66 (12) , indicating a rather strong distortion from the ideal octahedral shape. The conformation of the complex molecule is stabilized through a weak intramolecular hydrogen bond [3.099 (4) Å and 143 (3) ] between the N4-H4A donor and the O2 acceptor (Table 1) defining a six-membered ring with graphset notation S(6). Most coplanar with the aromatic ring is the N1O 2 nitro group [dihedral angle of 3.873 (3) ] while the carboxylate group is considerably twisted from the aromatic ring [dihedral angle = 19.332 (9) ]. The arrangement of the N2O 2 nitro group is intermediate between the latter two, the corresponding dihedral angle being 13.529 (6) .

Figure 2
The crystal packing of the coordination complex [Cd(DNBA) 2 (en) 2 )] showing N-HÁ Á ÁO hydrogen bonds as dashed lines. For clarity, H atoms not involved in hydrogen bonding are omitted.

Figure 3
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.  Groom et al., 2016) attested that over 300 crystal structures based on DNBA are registered. Among these structures, eleven compounds are monoligand complexes while 120 ones belong to mixed-ligand coordination compounds. There are two mixed-ligand complexes closely related to the [Cd(DNBA) 2 (en) 2 )] complex. The silver complexes with refcodes EQOKEA (Zhu et al., 2003) and EQOKEA01 (Qiu et al., 2005) consist of discrete and polymeric components. In the discrete component, Ag I is coordinated by two DNBA molecules in a monodentate mode whereas in the second component silver ions are associated by en ligands into polymeric chains. There are also DNBA, en and -NO 2 ligands in the Co I complex with refcode KICCEF (Sharma et al., 2007). In this complex, the metal ion is chelated by two en ligands, and one DNBA and one NO 2 molecules each in a monodentate mode.

Synthesis and crystallization
To an aqueous solution (2.5 ml) of Cd(CH 3 COO) 2 (0.115 g, 0.5 mmol) was slowly added an ethanol solution (4 ml) containing en (60 l) and DNBA (0.212 g, 1 mmol) under constant stirring. A colourless crystalline product was obtained at room temperature by slow solvent evaporation after 6 d. Single crystals for X-ray structure determination were selected from this product. Yield: 65%. Elemental analysis for C 18

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Bis(3,5-dinitrobenzoato-κO)bis(ethane-1,2-diamine-κ 2 N,N′)cadmium(II)
Crystal data [Cd(C 7   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. N-bound H atoms were located in a difference Fourier map and were refined with bond-length restraints of 0.92 (1)