Di-μ-iodido-bis(iodido{methyl 4-[(pyridin-2-ylmethylidene)amino]benzoate-κ2 N,N′}cadmium)

The complete binuclear molecule of the title compound, [Cd2I4(C14H12N2O2)2], is generated by the application of a centre of inversion. The Cd—I bond lengths of the central core are close and uniformly longer than the exocyclic Cd—I bond. The coordination sphere of the CdII atom is completed by two N atoms of a chelating methyl 4-[(pyridin-2-ylmethylidene)amino]benzoate ligand, and is based on a square pyramid with the terminal I atom in the apical position. The three-dimensional crystal packing is stabilized by C—H⋯O and C—H⋯π interactions, each involving the pyridine ring.


Comment
The title compound, (I), was investigated during the course of studies into the coordination chemistry of divalent zinc triad elements with (E)-N-(pyridin-2-ylmethylidene)arylamine ligands. These complexes were investigated primarily by X-ray crystallography and proton NMR but, also included some biological studies (Basu Baul, Kundu, Höpfl et al., 2013;Basu Baul, Kundu, Mitra et al. 2013).
The centrosymmetric binuclear compound, Fig. 1, features a central Cd 2 I 2 core that approximates a square as the µ 2 -I atoms form almost equivalent Cd-I bond lengths, each of which is longer than the terminal Cd-I bond, Table 1. The five-coordinate environment is completed by the chelating ligand which exhibits a twist as seen in the dihedral angle between the two rings of 30.78 (17)°. The coordination geometry approximates a square pyramid as judged by the value of τ = 0.13, compared with 0.0 and 1.0 for ideal square pyramidal and trigonal bipyramidal geometries, respectfully (Addison et al., 1984). In this description, the Cd atom lies 0.9208 (1) Å above the plane defined by the two µ 2 -I and chelating N atoms (r.m.s. deviation = 0.0690 Å) in the direction of the terminal I atom. As observed in related systems, the Cd-(pyridyl) bond length is shorter than the Cd-N(imino) bond. The ester group is twisted out of the plane of the benzene ring to which it is connected as seen in the value of the C9-C10-C13-O1 torsion angle of 161.5 (3)°.
The crystal packing is dominated by interactions involving the pyridyl residue, Table 2

Experimental
To a solution of pyridine-2-carboxaldehyde (0.10 g, 0.93 mmol) in ethanol (3 ml) was added a solution of methyl paminobenzoate (0.15 g, 0.99 mmol) in ethanol (2 ml). The mixture was stirred at ambient temperature for 30 min. To this reaction mixture, a solution of CdI 2 (0.36 g, 0.98 mmol) in methanol (20 ml) was added drop-wise under stirring conditions which resulted in the immediate formation of a yellow precipitate. The stirring was continued for 3 h and then the mixture was filtered. The residue was washed with methanol (3 x 5 ml) and dried in vacuo.

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H 0.95 to 0.98 Å, U iso (H) 1.2 to 1.5U eq (C)] and were included in the refinement in the riding model approximation. Two reflections, i.e. (1 0 0) and (-5 0 2), were omitted from the final refinement owing to poor agreement. The maximum and minimum residual electron density peaks of 0.58 and 1.04 e Å -3 , respectively, were located 0.69 Å and 0.49 Å from the I2 and I1 atoms, respectively.

Figure 1
Molecular structure of the centrosymmetric binuclear molecule of (I) showing atom-labelling scheme and displacement ellipsoids at the 50% probability level. The primed atom is related by the symmetry operation 1 -x, 1 -y, 1 -z.

Di-µ-iodido-bis(iodido{methyl 4-[(pyridin-2-ylmethylidene)amino]benzoate-κ 2 N,N′}cadmium)
Crystal data 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.