Bis[μ-4-(dimethylamino)benzoato]-κ3 O,O′:O;κ3 O:O,O′-bis{aqua[4-(dimethylamino)benzoato-κ2 O,O′](nicotinamide-κN 1)cadmium(II)}

In the centrosymmetric dimeric CdII title compound, [Cd2(C9H10NO2)4(C6H6N2O)2(H2O)2], each seven-coordinated CdII atom is chelated by the carboxylate groups of the two 4-(dimethylamino)benzoate (DMAB) anions; the two monomeric units are bridged through the two O atoms of the two carboxyl groups. In the crystal structure, intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. π–π contacts between the pyridine rings [centroid–centroid distance = 3.974 (1) Å] may further stabilize the structure. Weak C—H⋯π interactions are also observed.

Cg2 and Cg3 are the centroids of the C11-C16 and N3/C19-C23 rings, respectively. which they may find applications in biological systems (Antolini et al., 1982). Some benzoic acid derivatives, such as 4aminobenzoic acid, have been extensively reported in coordination chemistry, as bifunctional organic ligands, due to the varieties of their coordination modes (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000). Nicotinamide

D-HÁ
(NA) is one form of niacin. A deficiency of this vitamin leads to loss of copper from the body, known as pellagra disease.
The structure-function-coordination relationships of the arylcarboxylate ion in Cd II complexes of benzoic acid derivatives may also 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 as in Mn(II) complexes (Shnulin 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). We report herein the synthesis and the structure of the title compound, (I).
The title compound, (I), consists of dimeric units located around a crystallographic symmetry centre and made up of two Cd cations, four 4-(dimethylamino)benzoato (DMAB) anions, two nicotinamide (NA) ligands and two water molecules ( Fig. 1). Each Cd(II) unit is chelated by the carboxylate O atoms of the two DMAB anions, and the two monomeric units are bridged through the two oxygen atoms of the two carboxylate groups about an inversion center. The coordination number of each Cd II atom is seven. The Cd1···Cd1 i distance is 3.8121 (2) Å and O4-Cd1-O4 i angle is 76.87 (4)° (symmetry code: (i) -x, -y, 1 -z).
The average Cd-O bond length (Table 1)  (where Asp is acetylsalicylate and py is pyridine) (Greenaway et al., 1984).
The dihedral angles between the planar carboxylate groups and the adjacent benzene rings A (C2-C7) and B (C11-C16) are 11.48 (17)  supplementary materials sup-2 In the crystal structure, intermolecular O-H···O, N-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. The π-π contact between the pyridine rings, Cg3-Cg3 i [symmetry code: (i) 1 -x, -1 -y, 1 -z, where Cg3 is the centroid of the ring C (N3/C19-C23)] may further stabilize the structure, with centroid-centroid distance of 3.974 (1) Å. There also exist two weak C-H···π interactions (Table 2).

Experimental
The title compound was prepared by the reaction of 3CdSO 4 .H 2 O (1.28 g, 5 mmol) in H 2 O (30 ml) and NA (1.22 g, 10 mmol) in H 2 O (20 ml) with sodium 4-(dimethylamino)benzoate (1.88 g, 10 mmol) in H 2 O (150 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving colorless single crystals.

Refinement
Atoms H61 and H62 were located in a difference Fourier map and refined isotropically. The remaining H atoms were positioned geometrically with N-H = 0.86 Å (for NH 2 ) and C-H = 0.93 and 0.96 Å for aromatic and methyl H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C,N), where x = 1.5 for methyl H and x = 1.2 for all other H atoms. Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level [symmetry code: (') -x, -y, 1 -z]. Hydrogen atoms are omitted for clarity. Atomic displacement parameters (Å 2 )