Crystal structure of trans-diaquabis(4-cyanobenzoato-κO)bis(N,N-diethylnicotinamide-κN)cadmium

The CdII atom in the title complex, [Cd(C10H14N2O)2(C8H4NO2)2(H2O)2], is located on an inversion centre and is coordinated by an N2O4 donor set from pairs of water, 4-cyanobenzoate and N,N-diethylnicotinamide ligands.

The structure-function-coordination relationships of the arylcarboxylate ion in Cd II complexes of benzoic acid derivatives may change depending on the nature and position of the substituent groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of synthesis Nadzhafov et al., 1981;Antsyshkina et al., 1980;Adiwidjaja et al., 1978). When pyridine and its derivatives are used instead of water molecules, the structure is completely different (Catterick et al., 1974). In this context, we synthesized a Cd II -containing compound with 4-cyanobenzoate (CB) and DENA ligands, namely trans-diaquabis(4-cyanobenzoato-O)bis(N,N 0 -di- ISSN 2056-9890 ethylnicotinamide-N)cadmium, [Cd(CB) 2 (DENA) 2 (H 2 O) 2 ], and report herein its crystal structure.

Structural commentary
The asymmetric unit of the mononuclear title complex contains one Cd II atom located on an inversion centre, one CB ligand, one DENA ligand as well as one water molecule, all ligands coordinating to the Cd II atom in a monodentate mode (Fig. 1). The two carboxylate O atoms (O2 and O2 i ) [symmetry code: (i) Àx, Ày, Àz] of the two symmetry-related monodentate CB anions and water O atoms (O4 and O4 i ) form a slightly distorted square-planar arrangement around the Cd1 atom, while the slightly distorted octahedral coordination sphere is completed by the two pyridine N atoms (N1 and N1 i ) of two DENA ligands (Fig. 1) (2) Å ] are 0.015 (2) Å longer than those of the non-coordinating ones, indicating delocalized bonding arrangements rather than localized single and double bonds. The dihedral angle between the carboxylate group (O1/O2/ C1) and the adjacent benzene (C2-C7) ring is 8.75 (16) , while the benzene and pyridine (N1/C9-C13) rings are oriented at a dihedral angle of 57.83 (5) .

Figure 2
Part of the supramolecular chain of the title compound.

Synthesis and crystallization
The title compound was prepared by the reaction of CdSO 4 Á-8/3H 2 O (0.64 g, 2.5 mmol) in H 2 O (50 ml) and diethylnicotinamide (0.89 g, 5 mmol) in H 2 O (10 ml) with sodium 4cyanobenzoate (0.85 g, 5 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving colourless single crystals.

Refinement
Experimental details including the crystal data, data collection and refinement are summarized in Table 2. Atoms H41 and H42 (for H 2 O) were located in a difference Fourier map and were refined freely. The C-bound H atoms were positioned geometrically with C-H = 0.93, 0.97 and 0.96 Å , for aromatic, methylene and methyl H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = k Â U eq (C), where k = 1.5 for methyl H atoms and k = 1.2 for aromatic and methylene H-atoms. Computer programs: APEX2 and SAINT (Bruker, 2012), SHELXS97 and SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows and WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

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. 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 > 2sigma(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.