Crystal structures of di-bromido-{N-[(pyridin-2-yl-κN)methyl-idene]picolinohydrazide-κ2N',O}cadmium methanol monosolvate and di-iodido{N-[(pyridin-2-yl-κN)methyl-idene]picolinohydrazide-κ2N',O}cadmium.

The title compounds, [CdBr2(C12H10N4O)]·CH3OH, (I), and [CdI2(C12H10N4O)], (II), are cadmium bromide and cadmium iodide complexes of the ligand (E)-N'-(pyridin-2-yl-methyl-ene)picolinohydrazide. Complex (I) crystallizes as the methanol monosolvate. In both compounds, the Cd2+ cation is ligated by one O atom and two N atoms of the tridentate ligand, and by two bromide anions forming a Br2N2O penta-coordination sphere for (I), and by two iodide anions forming an I2N2O penta-coordination sphere for (II), both with a distorted square-pyramidal geometry. In the crystal of complex (I), mol-ecules are linked by pairs of N-H⋯O and O-H⋯Br hydrogen bonds, involving the solvent mol-ecule, forming dimeric units, which are linked by C-H⋯Br hydrogen bonds forming layers parallel to (101). In the crystal of complex (II), mol-ecules are linked by N-H⋯I hydrogen bonds, forming chains propagating along [010]. In complex (II), measured at room temperature, the two iodide anions are each disordered over two sites; the refined occupancy ratio is 0.75 (2):0.25 (2).

The title compounds, [CdBr 2 (C 12 H 10 N 4 O)]ÁCH 3 OH, (I), and [CdI 2 (C 12 H 10 N 4 O)], (II), are cadmium bromide and cadmium iodide complexes of the ligand (E)-N 0 -(pyridin-2-ylmethylene)picolinohydrazide. Complex (I) crystallizes as the methanol monosolvate. In both compounds, the Cd 2+ cation is ligated by one O atom and two N atoms of the tridentate ligand, and by two bromide anions forming a Br 2 N 2 O pentacoordination sphere for (I), and by two iodide anions forming an I 2 N 2 O pentacoordination sphere for (II), both with a distorted square-pyramidal geometry. In the crystal of complex (I), molecules are linked by pairs of N-HÁ Á ÁO and O-HÁ Á ÁBr hydrogen bonds, involving the solvent molecule, forming dimeric units, which are linked by C-HÁ Á ÁBr hydrogen bonds forming layers parallel to (101). In the crystal of complex (II), molecules are linked by N-HÁ Á ÁI hydrogen bonds, forming chains propagating along [010]. In complex (II), measured at room temperature, the two iodide anions are each disordered over two sites; the refined occupancy ratio is 0.75 (2):0.25 (2).

Chemical context
The cadmium(II) ion, has a d 10 electronic configuration and exhibits a variety of coordination geometries and modes. Hydrazone ligands are one of the most important classes of flexible and versatile polydentate ligands and show very high efficiency in chelating transition metal ions (Afkhami et al., 2017a). Hydrazone ligands obtained from 2-pyridine carboxylic acid can act as ditopic ligands via two different donor sites (a tridentate coordination pocket and through an Ndonor pyridine group), and have the potential to form monoand multinuclear structures (Afkhami et al., 2017b). Herein, we report on the crystal structures of two new Cd II complexes based on the tridentate hydrazone ligand, (E)-N 0 -(pyridin-2ylmethylene)picolinohydrazide, obtained by condensation of an equimolar mixture of 2-pyridinecarbaldehyde and picolinic acid hydrazide in methanol.

Structural commentary
The molecular structures of compounds (I) and (II) are shown in Figs. 1 and 2, respectively. In compound (I), the ligand is almost planar with a dihedral angle between the pyridine rings ISSN 2056-9890 of 6.9 (3) . The Cd1-Br1 and Cd1-Br2 bond lengths are 2.5585 (6) and 2.5490 (7) Å , respectively, and the Cd1-N2 bond length is 2.336 (4) Å . Atom Cd1 is ligated by one O atom (O1) and two N atoms (N1 and N2) of the tridentate ligand, and by two bromide anions, hence the Cd 2+ cation has a fivefold Br 2 N 2 O coordination sphere with a distorted shape and a 5 value of 0.33 ( 5 = 0 for an ideal square-pyramidal coordination sphere, and = 1 for an ideal trigonal-pyramidal coordination sphere; Addison et al., 1984).
In compound (II), the ligand is also almost planar with a dihedral angle between the pyridine rings of 8.0 (2) . The two iodide anions are each disordered over two sites; the refined occupancy ratio is 0.75 (2):0.25 (2) for atoms I1A/I2A:I1B/I2B. Considering the major components only, the Cd1-I1A and Cd1-I2A bond lengths are 2.736 (3) and 2.7128 (19) Å , respectively, and the Cd1-N2 bond length is 2.336 (3) Å . Atom Cd1 is ligated by one O atom (O1) and two N atoms (N1 and N2) of the tridentate ligand, and by two iodide anions. Atom Cd1 has a fivefold I 2 N 2 O coordination sphere with a distorted shape and a 5 value of 0.28.

Supramolecular features
In the crystal of compound (I), molecules are linked by pairs of N-HÁ Á ÁO and O-HÁ Á ÁBr hydrogen bonds, involving the solvent molecule, forming dimeric units, which are linked by C-HÁ Á ÁBr hydrogen bonds forming layers parallel to (101); see Table 1 and Fig. 3. In the crystal of complex (II), molecules are linked by N-HÁ Á ÁI hydrogen bonds forming chains propagating along [010]; see Table 2 and Fig. 4.

Synthesis and crystallization
A solution of the ligand N 0 -(pyridin-2-ylmethylene)picolinohydrazide (0.151 g, 0.5 mmol) in 30 ml of methanol was treated with a methanolic solution of the appropriate cadmium(II) salt (0.5 mmol); CdBr 2 for complex (I) and CdI 2 for (II). The solutions were heated under reflux for 4 h and then allowed to stand at room temperature. After slow evaporation of the solvent, single crystals separated out. They were collected, washed with ether and dried over P 4 O 10 in vacuum. A view normal to (101) of the crystal packing of compound (I). The hydrogen bonds are shown as dashed lines (see Table 1). For clarity, only the H atoms involved in hydrogen bonding have been included.

Figure 4
A view along the a axis of the crystal packing of compound (II). The hydrogen bonds are shown as dashed lines (see Table 2). For clarity, only the H atoms involved in hydrogen bonding and only the major components of the disordered I atoms have been included.

Refinement
Crystal data, data collection and structure refinement details for compounds (I) and (II) are summarized in Table 3. For complex (I), measured at 130 K, H atoms were placed in calculated positions (C-H = 0.95-0.98 Å , N-H = 0.88 Å and O-H = 0.84 Å ) and included in the refinement in the ridingmodel approximation, with U iso (H) = 1.5U eq (O) and 1.2U eq (N,C) for other H atoms. Owing to poor agreement, two reflections, (4 4 6 and 7 10 3), were omitted from the final cycles of refinement. For complex (II), measured at 296 K, the C-bound H atoms were placed in calculated positions (C-H = 0.93 Å ) and included in the refinement in the riding-model approximation, with U iso (H) = 1.2U eq (C). The N-bound H atoms were located in a difference-Fourier map but were refined with a distance restraint of N-H = 0.86 (4) Å with U iso (H) = 1.2U eq (N). In complex (II), the two iodide anions (I1 and I2) are each disordered over two sites, and their siteoccupation factors refined to 0.75 (2):0.25 (2).
Plus (Bruker, 2016) for (II). Program(s) used to solve structure: SHELXS2014/7 (Sheldrick, 2008)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.63 e Å −3 Δρ min = −0.76 e Å −3 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.

(II) Diiodido{N-[(pyridin-2-yl-κN)methylidene]picolinohydrazide-κ 2 N′,O}cadmium
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.