Crystal structure and Hirshfeld surface analysis of diiodido{N′-[(E)-(phenyl)(pyridin-2-yl-κN)methylidene]pyridine-2-carbohydrazide-κ2 N′,O}cadmium(II)

The title compound contains two molecules in the asymmetric unit: both feature a distorted square-pyramidal CdN2OI2 coordination polyhedron and an intramolecular N—H⋯N hydrogen bond.


Chemical context
Hydrazone ligands show high efficiency in chelating transition-metal ions (Afkhami et al., 2017a); such ligands obtained from pyridine carboxylic acids can act as ditopic ligands because of their two different donor sites, including an Ndonor pyridine group and a tridentate coordination pocket, and have the potential to form mono-, di-and multinuclear structures (Afkhami et al., 2017b). In this work, we report the synthesis, crystal structure and Hirshfeld surface analysis of the title Cd II complex, (I), containing the tridentate hydrazone ligand N 0 -[(E)-(pyridin-2-yl)methylidene]pyridine-2-carbohydrazide.

Structural commentary
The molecular structure of (I), which contains two [CdI 2 (C 18 H 14 N 4 O)] molecules, A (with Cd1) and B (with Cd2), in the asymmetric unit is shown in Fig. 1. In both molecules, the Cd atom is pentacoordinated to two N, one O and two I ISSN 2056-9890 atoms ( Table 1). The Addison parameter (Addison et al., 1984) quantifies the distinction between trigonal-bipyramidal (ideally = 1) and square-pyramidal (ideally = 0) geometries. For the title complex, = 0.11 for A and 0.09 for B, indicating a distorted square-pyramidal geometry (Fig. 2).

Figure 2
View of the coordination polyhedra about the Cd atoms in (I), showing their distorted square-based pyramidal geometries. Table 2 Hydrogen-bond geometry (Å , ).

Figure 3
Partial packing diagram of (I) showing the A and B molecules linked by a pair ofstacking interactions. Symmetry operation: (iv) Àx, 1 À y, 1 À z.

Synthesis and crystallization
The N 0 -[(E)-(pyridin-2-yl)methylidene]pyridine-2-carbohydrazide ligand was synthesized according to the literature method (Abedi et al., 2016). To prepare single crystals of (I), an equimolar mixture (1.0 mmol) of the hydrazone ligand and metal salt [CdI 2 ] were placed in the main arm of a branched tube, and methanol was carefully added to fill the arms (Khandar et al., 2015). The tube was sealed and the mixturecontaining arm was immersed in an oil bath at 333 K while the branched arm was kept at room temperature. After a couple of days, yellow prisms of (I) had been deposited in the cooler arm and these were isolated, filtered off, washed with diethyl ether and dried over P 4 O 10 in vacuo.

Diiodido{N′-[(E)-(phenyl)(pyridin-2-yl-κN)methylidene]pyridine-2-carbohydrazide-κ 2 N′,O}cadmium(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.