Iodido{4-phenyl-1-[1-(1,3-thiazol-2-yl-κN)ethylidene]thiosemicarbazidato-κ2 N′,S}{4-phenyl-1-[1-(1,3-thiazol-2-yl)ethylidene]thiosemicarbazide-κS}cadmium(II)

In the title complex, [Cd(C12H11N4S2)I(C12H12N4S2)], the CdII ion is pentacoordinated by two thiosemicarbazone ligands (one neutral and the other anionic) and one iodide ion in a distorted square pyramidal (τ = 0.35) geometry. The central ion is coordinated by the thiazole N atom, the thioureido N and the S atom of the deprotonated thiosemicarbazone ligand. The other ligand is linked with the central ion through the C=S group. The deprotonated ligand intramolecularly hydrogen bonds to the thiazole ring N atom, while the ligand forms an intermolecular hydrogen bond to the thiolate S atom of the second ligand. The deprotonation of the tridentate ligand and its coordination to the CdII ion via the S atom strikingly affects the C—S bond lengths. The C—S bond lengths in the neutral and deprotonated ligands in the metal complex are 1.709 (3) and 1.748 (2) Å, respectively, whereas it is 1.671 (3) Å in the free ligand. In the metal complex, the Cd—S distances are 2.6449 (6) and 2.5510 (6) Å. The Cd—I bond length is 2.7860 (2) Å.

In the title complex, [Cd(C 12 H 11 N 4 S 2 )I(C 12 H 12 N 4 S 2 )], the Cd II ion is pentacoordinated by two thiosemicarbazone ligands (one neutral and the other anionic) and one iodide ion in a distorted square pyramidal ( = 0.35) geometry. The central ion is coordinated by the thiazole N atom, the thioureido N and the S atom of the deprotonated thiosemicarbazone ligand. The other ligand is linked with the central ion through the C S group. The deprotonated ligand intramolecularly hydrogen bonds to the thiazole ring N atom, while the ligand forms an intermolecular hydrogen bond to the thiolate S atom of the second ligand. The deprotonation of the tridentate ligand and its coordination to the Cd II ion via the S atom strikingly affects the C-S bond lengths. The C-S bond lengths in the neutral and deprotonated ligands in the metal complex are 1.709 (3) and 1.748 (2) Å , respectively, whereas it is 1.671 (3) Å in the free ligand. In the metal complex, the Cd-S distances are 2.6449 (6) and 2.5510 (6) Å . The Cd-I bond length is 2.7860 (2) Å .

Related literature
For properties of thiosemicarbazones and Cd complexes, see: Casas et al. (2000); Milczarska et al. (1998); Venkatraman et al.  Arumugam et al. (2011). For a description of the geometry of complexes with five-coordinate metal atoms, see: Addison et al. (1984).

Fronczek Comment
Heterocyclic thiosemicarbazones are versatile ligands forming complexes with a variety of transition metal ions. These ligands and their metal complexes are found to exhibit cytotoxic effects (Casas et al., 2000, Milczarska et al., 1998. Among several metals ions that complex with thiosemicarbazones, cadmium (II) has received less attention (Viñuelas-Zahínos et al. 2011). In continuation of our structural studies of metal thiosemicarbazones (Venkatraman et al., 2009;Dasary et al., 2011;Arumugam et al. 2011), we herein report the Cd II complex of 2-acetyl thiazole N(4) phenyl thiosemicarbazone. The title complex is obtained from the reaction of cadmium (II) iodide with two equivalents of neutral ligands in methanol. This complex is an isomorph of the Hg complex reported by us earlier . In this complex, the Cd II is tridentately attached to one of the deprotonated ligand through the donor groups of N1, N2 and S2, while the metal ion is singly coordinated to the other ligand via S4. As shown in Fig. 1, one iodide is found to coordinate with the central metal ion from other side forming a pentacoodinated complex (τ= 0.35) with a pyramidal square planar geometry (Addison et al., 1984). The deprotonated ligand is twisted due to intra-molecularly hydrogen bonds (N7H···N5), while the ligand forms an intermolecular hydrogen bond via S2 with NH group (N4) from the other ligand (Fig. 2). The deprotonation of the tridentate ligand and its coordination to the Cd via the S atom strikingly affects the C-S bond lengths. The C-S bond distances in the neutral and deprotonated ligands in the metal complex are 1.709 (3) Å and 1.748 (2) Å respectively whereas it is 1.671 (3) Å in the free ligand. In the metal complex, the Cd-S distances are 2.6449 (6) Å, 2.5510 (6) Å. The Cd-I bond distance is 2.7860 (2) Å. The torsion angles (N2-N3-C6-N4), and (N6-N7-C18 -N8) for two ligands is 179.48 (8)° and 8.5 (3)° respectively. Hydrogen bonding details are given in Table 1.

Experimental
To a boiling methanol solution (50 ml) containing 2-acetylthiazole phenylthiosemicarbazone (1.38 g, 5 mmol) was added an equimolar of cadmium (II) iodide (1.38 g, 5 mmol) in 20 ml of methanol solution (Venkatraman et al., 2009)). The mixture was refluxed for 3 to 4 h under stirring. The resulting bright yellow solid obtained was filtered and dried (65% yield). Crystals suitable for diffraction were obtained from the mother liquor at ambient temperature after two days in a methanol-DMF mixture (5:1 V/V).

Refinement
H atoms on C were placed in idealized positions with C-H distances 0.98 Å for methyl groups and 0.95 Å for others, and thereafter treated as riding. Coordinates of the NH hydrogen atoms were refined, with all N-H distances restrained supplementary materials sup-2 Acta Cryst. (2013). E69, m246-m247 to be equal. U iso for H were assigned as 1.2 times U eq of the attached atoms (1.5 for methyl).

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.  Intra-and inter-molecular H-hydrogen bonding of the compound (1) viewed along b axis.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq