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

In the crystal, the title centrosymmetric ZnII complex molecules are linked by O—H⋯O hydrogen bonds into supramolecular chains propagating along the [110] direction.

In the title complex, [Zn(C 8 H 4 NO 2 ) 2 (C 10 H 14 N 2 O) 2 (H 2 O) 2 ], the Zn II cation, located on an inversion centre, is coordinated by two water molecules, two 4-cyanobenzoate (CB) anions and two diethylnicotinamide (DENA) ligands in a distorted N 2 O 4 octahedral geometry. In the molecule, the dihedral angle between the planar carboxylate group and the adjacent benzene ring is 9.50 (14) , while the benzene and pyridine rings are oriented at a dihedral angle of 56.99 (5)

Chemical context
Nicotinamide (NA) is one form of niacin. A deficiency of this vitamin leads to loss of copper from the body, known as pellagra disease. Victims of pellagra show unusually high serum and urinary copper levels (Krishnamachari, 1974). The nicotinic acid derivative N,N-diethylnicotinamide (DENA) is an important respiratory stimulant (Bigoli et al., 1972). The structures of some complexes obtained from the reactions of transition metal(II) ions with NA and DENA as ligands, e.g.
The structure-function-coordination relationships of the arylcarboxylate ion in Zn II complexes of benzoic acid derivatives may change depending on the nature and position of the substituted 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 Zn II -containing compound with 4-cyanobenzoate (CB) and DENA ligands, namely trans-diaquabis(4-cyanobenzoato-O)bis(N,N-diethylnicotinamide-N)zinc(II), [Zn(DENA) 2 (CB) 2 (H 2 O) 2 ], and report herein its crystal structure.

Structural commentary
The asymmetric unit of the crystal structure of the title complex contains one Zn II atom located on an inversion centre, one 4-cyanobenzoate (CB) ligand, one N,N-diethylnicotinamide (DENA) ligand and one water molecule, all ligands coordinating to the Zn II atom in a monodentate manner (Fig. 1).
The two carboxylate O atoms (O2 and O2 i ) of the two symmetry-related monodentate CB anions and the two symmetry-related water O atoms (O4 and O4 i ) around the Zn1 atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination sphere is completed by the two pyridine N atoms (N2 and N2 i ) of the two symmetry-related monodentate DENA ligands in the axial positions [symmetry code: (i) Àx, Ày, Àz] (Fig. 1 The dihedral angle between the planar carboxylate group (O1/O2/C1) and the adjacent benzene ring (C2-C7) is 9.50 (14) , while the benzene and pyridine (N2/C9-C14) rings are oriented at a dihedral angle of 56.99 (5) .

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

Synthesis and crystallization
The title compound was prepared by the reaction of ZnSO 4 Á7H 2 O (1.44 g, 5 mmol) in H 2 O (50 ml) and diethylnicotinamide (1.78 g, 10 mmol) in H 2 O (10 ml) with sodium 4cyanobenzoate (1.69 g, 10 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving translucent intense colourless single crystals.

Refinement
The 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. Part of the crystal structure. Intra-and intermolecular (O-H w Á Á ÁO c and O-H w Á Á ÁO DENA , respectively) hydrogen bonds are shown as dashed lines (see Table 1). The non-bonding H atoms have been omitted for clarity.

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.