Diaquabis(N,N-diethylnicotinamide-κN 1)bis(4-formylbenzoato-κO 1)zinc

In the title complex, [Zn(C8H5O3)2(C10H14N2O)2(H2O)2], the ZnII cation is located on an inversion center and is coordinated by two 4-formylbenzoate anions, two N,N-diethylnicotinamide (DENA) ligands and two water molecules. The four O atoms in the equatorial plane around the ZnII cation form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the DENA ligands in the axial positions. The dihedral angle between the carboxylate group and the adjacent benzene ring is 2.96 (11)°, while the pyridine ring and the benzene ring are oriented at a dihedral angle of 79.26 (4)°. The coordinating water molecule links with the carboxylate group via an intramolecular O—H⋯O hydrogen bond. In the crystal, O—H⋯O and weak C—H⋯O hydrogen bonds link the molecules into a three-dimensional supramolecular network. A π–π contact between the parallel pyridine rings of adjacent molecules may further stabilize the crystal structure [centroid–centroid distance = 3.5654 (8) Å].

In the title mononuclear complex, Zn II cation is located on an inversion center and is coordinated by two 4-formylbenzoate (FB) anions, two N,N-diethylnicotinamide (DENA) ligands and two water molecules, all ligands coordinating in a monodentate manner (Fig. 1) In the title complex, the four symmetry related O atoms (O2, O2′, O5 and O5′) in the equatorial plane around the Zn II ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two symmetry related N atoms of the DENA ligands (N1 and N1′) in the axial positions. The near equalities of the C1-O1 [1.2533 (16) Å] and C1-O2 [1.2623 (16) Å] bonds in the carboxylate group indicate delocalized bonding arrangement, rather than localized single and double bonds. The Zn-O bond lengths are 2.1128 (9) Å (for benzoate oxygens) and 2.1289 (10) Å (for water oxygens), and the Cu-N bond length is 2.1452 (11) Å, close to standard values (Allen et al., 1987). The Zn atom is displaced out of the mean-plane of the carboxylate group (O1/C1/O2) by 0.8455 (1) Å. The dihedral angle between the planar carboxylate group and the adjacent benzene ring A (C2-C7) is 2.96 (11)°. The benzene A (C2-C7) and the pyridine B (N1/C9-C13) rings are oriented at a dihedral angle of A/B = 79.26 (4)°. The coordinating water molecule links with the carboxylate group via an O-H···O hydrogen bond (Table 1).
In the crystal, intermolecular O-H···O and weak C-H···O hydrogen bonds (Table 1) link the molecules into a threedimensional supramolecular network, in which they may be effective in the stabilization of the structure. The π-π contact between the pyridine rings, Cg2-Cg2 i [symmetry code: (i) 1 -x, 1 -y, -z, where Cg2 is the centroid of the ring B (N1/C9-C13)] may further stabilize the structure, with centroid-centroid distance of 3.5654 (8) Å].

Experimental
The title compound was prepared by the reaction of ZnSO 4 .H 2 O (0.90 g, 5 mmol) in H 2 O (30 ml) and DENA (1.78 g, 10 mmol) in H 2 O (10 ml) with sodium 4-formylbenzoate (1.72 g, 10 mmol) in H 2 O (100 ml) at room temperature. The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving colorless single crystals.

Refinement
Atoms H8 (for CH) and H51 and H52 (for H 2 O) were located in a difference Fourier map and were refined freely. The Cbound 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 × U eq (C), where k = 1.5 for methyl H-atoms and k = 1.2 for all other H-atoms.

Figure 1
The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level [symmetry code: (′) -x, -y, -z]. 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.