Synthesis, crystal structure and Hirshfeld surface analysis of a cadmium complex of naphthalene-1,5-disulfonate and o-phenylenediamine

The molecular and crystal structure of a cadmium complex of naphthalene-1,5-disulfonate and o-phenylenediamine was studied and Hirshfeld surfaces and fingerprint plots were generated to investigate the various intermolecular interactions.


Chemical context
Cadmium is widely used in the fabrication of rechargeable batteries, in alloys, coatings (electroplating), solar cells, plastic stabilizers, phosphate fertilizers, and pigments (Omar et al., 2014;Morrow, 2010;Indumathi et al., 2011;Kapadnis et al., 2020;Wakkaf et al., 2020;Roberts, 2014;Cesaratto et al., 2014).Given its common use, cadmium is now spreading widely in the environment (Kumar et al., 2019;Wang et al., 2023) and, due to its toxicity, it is necessary to prevent the technogenic spread of cadmium and its harmful consequences.
When it comes to complex formation, organic ligands with multiple donor centers that form chelates play a crucial role.Stable complexes are obtained by the formation of a ring consisting of five or six members, including a metal atom in the ring.Additionally, when the bidentate ligand is involved in coordination with the central atom by forming a fivemembered ring, it further increases the stability of the complex (Lawrance, 2010).The conformational change of fiveand six-membered diamine chelate rings in metal complexes has been thoroughly documented (Corey et al., 1959;Gollogly et al., 1967;Ma et al., 2005Ma et al., , 2012)).In this regard, the ophenylenediamine (opda) ligand has been extensively studied as a linking agent that effectively forms a chelating ring with a variety of metal cations.Developing metal ion sorbents utilizing these organic ligands is both economically and practically efficient.We present a report on the crystal structure and Hirshfeld surface analysis of a newly synthesized Cd complex salt of naphthalene-1,5-disulfonate with o-phenylenediamine (opda) as its base.

Structural commentary
The complex salt [Cd(opda) 4 ](C 10 H 6 O 6 S 2 ) crystallizes in the monoclinic system, space group C2/c.The Cd atom occupies a special position with twofold symmetry (Wyckoff position 4e).The midpoint of the naphthalene-1,5-disulfonate anion lies on a center of inversion (Wyckoff position 4b).Therefore, the asymmetric unit consists of one half of the complex cation and anion.
Fig. 1 shows the coordination environment of the Cd atom and the hydrogen bonds between the amine hydrogens and the oxygen atoms of the anion.The Cd atom coordinates six nitrogen atoms which come from two o-phenylenediamine molecules and their two symmetry-related counterparts [symmetry operation: (i) 1 À x, y, 3 2 À z].The naphthalene-1,5disulfonate anion is completed by atoms related by 1 À x, 2 À y, 1 À z [symmetry operation: (ii)].Two of the ophenylenediamine ligands are coordinated in a chelating fashion while the other two form monodentate bonds.The chelating and monodentate ligands are located in cis positions.The complex exhibits a distorted octahedral coordination sphere for the metal atom due to the reduction of the N1-Cd1-N2 angle [70.41 (6) � ].This value is similar to those found in other cadmium complexes reported by several authors (Gonzalez Guillen et al., 2018;Malinina et al., 2007;Rahman et al., 2017;Supriya, 2009) where a chelate ring is observed.The largest bond angle between atoms in the basal plane in this polyhedron is 101.57(6) � for N1 i -Cd1-N3.Distortions are also observed in the angles between opposite vertex atoms.A value of 162.11 (10) � is observed for N1 i -Cd1-N1 and 170.30(6) � for N2-Cd1-N3 i and N2 i -Cd1-N3.All Cd1-N bonds have very close values with the maximum difference of only 0.0842 A ˚.The chelating coordination mode slightly affects the positions of the N and C atoms in the opda ligands.The opda ligands are approximately planar, with a maximum deviation from the least-squares plane of 0.003 A ˚for atom C12 in the monodentate one (r.m.s.deviation 0.002 A ˚) and 0.005 A ˚for atom C1 in the bidentate one (0.002A ˚r.m.s.deviation).The dihedral angle between the main planes of the phenyl ring (C1-C6 or C7-C12) and the N-C-C-N fragment is 4.16 (12) � in the bidentate ligand and 1.73 (13) � in the monodentate ligand.

Synthesis and crystallization
Ethanol/water 1:1 (10 mL) solutions of Cd(CH 3 COO) 2 •2H 2 O (0.266 g, 0.001 mol) and sodium naphthalene-1,5-disulfonate (0.332 g, 0.001 mol) were combined.To the obtained solution, a 10 ml ethanol solution of o-phenylenediamine (opda) (0.432 g, 0.004 mol) was added dropwise and then stirred at 323 K for 30 minutes.The final solution was left to crystallize and X-ray quality single crystals were produced after 15 days by slow evaporation of the solvent.

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.

32Figure 1
Figure 1 Molecular structure of the title compound.The hydrogen bond is indicated by a dashed line.Displacement ellipsoids are plotted at the 30% probability level.[Symmetry codes:(i) 1 À x, 2 À y, 1 À z; (ii) 1 À x, y, 3/2 -z.] Figure 3View of the molecular packing showing the hydrogen-bonding interactions that extend along the c-axis direction.

Figure 5
Figure 5Contributions of the various contacts to the two-dimensional fingerprint plots built using the Hirshfeld surfaces of the [Cd(opda) 4 ] 2+ cation (at the top) and the [naphthalene-1,5-disulfonate] 2À anion (at the bottom).

Table 2
Experimental details.