Diaquabis[4-(dimethylamino)benzoato-κO]bis(nicotinamide-κN 1)zinc(II) dihydrate

In the centrosymmetric title structure, [Zn(C9H10NO2)2(C6H6N2O)2(H2O)2]·2H2O, the ZnII cation, located on an inversion center, is coordinated by two 4-(methylamino)benzoate anions, two nicotinamide ligands and two water molecules in a slightly distorted octahedral geometry. The dihedral angle between the carboxylate group and the attached benzene ring is 3.09 (9)°, while the pyridine and benzene rings are oriented at a dihedral angle of 77.10 (4)°. The uncoordinated water molecule is linked to nicotinamide ligands by O—H⋯O hydrogen bonds. In the crystal, intermolecular N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. A weak N—H⋯π interaction also occurs.

In the centrosymmetric title structure, [Zn(C 9 H 10 NO 2 ) 2 (C 6 H 6 -N 2 O) 2 (H 2 O) 2 ]Á2H 2 O, the Zn II cation, located on an inversion center, is coordinated by two 4-(methylamino)benzoate anions, two nicotinamide ligands and two water molecules in a slightly distorted octahedral geometry. The dihedral angle between the carboxylate group and the attached benzene ring is 3.09 (9) , while the pyridine and benzene rings are oriented at a dihedral angle of 77.10 (4) . The uncoordinated water molecule is linked to nicotinamide ligands by O-HÁ Á ÁO hydrogen bonds. In the crystal, intermolecular N-HÁ Á ÁO, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network. A weak N-HÁ Á Á interaction also occurs.

Comment
As a part of our ongoing investigation on transition metal complexes of nicotinamide (NA), one form of niacin (Krishnamachari, 1974), and/or the nicotinic acid derivative N,N-diethylnicotinamide (DENA), an important respiratory stimulant (Bigoli et al., 1972), the title compound was synthesized and its crystal structure is reported herein.
The title compound, (I), is a mononuclear complex, where the Zn II ion is located on a crystallographic inversion center.
In the crystal structure, intermolecular N-H···O, O-H···O, and C-H···O hydrogen bonds (Table 2) link the molecules into a three-dimensional network, in which they may be effective in the stabilization of the structure. There also exists a weak N-H···π interaction (Table 2).

Experimental
The title compound was prepared by the reaction of ZnSO 4 .H 2 O (0.90 g, 5 mmol) in H 2 O (50 ml) and nicotinamide (1.22 g, 10 mmol) in H 2 O (30 ml) with sodium 4-dimethylaminobenzoate (1.88 g, 10 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving colorless single crystals.

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.