Crystal structure of poly[bis(μ-nicotinamide-κ2 N 1:O)bis(μ-4-nitrobenzoato-κ2 O 1:O 1′)zinc]

The asymmetric unit of the title zinc(II) coordination polymer contains two 4-nitrobenzoate (NB) anions and two nicotinamide (NA) ligands. Only one of the two NB anions and one of the two NA ligands bridge adjacent ZnII ions through eight- and 12-membered rings, respectively, forming polymeric chains running along the a-axis direction.


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). Transition metal complexes with biochemical molecules show interesting physical and/or chemical properties, through which they may find applications in biological systems (Antolini et al., 1982). Some benzoic acid derivatives, such as 4-aminobenzoic 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).
The structure-function-coordination relationships of the arylcarboxylate ion in Zn II complexes of benzoic acid derivatives 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). ISSN 2056-9890
The three carboxylate O atoms (O2, O5 and O6) of the three NB anions and one O atom (O10) of one of the two NA ligands in the equatorial plane around the Zn II cation form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two pyridine N atoms (N3 and N5) of the two NA ligands in the axial positions (Table 1  Symmetry codes: (i) Àx þ 2; Ày; Àz; (ii) Àx þ 1; Ày; Àz.

Synthesis and crystallization
The title compound was prepared by the reaction of ZnSO 4 ÁH 2 O (0.89 g, 5 mmol) in H 2 O (25 ml) and nicotinamide (1.22 g, 10 mmol) in H 2 O (25 ml) with sodium 4-nitrobenzoate (1.90 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 yellow block-like crystals.

Refinement
The experimental details including the crystal data, data collection and refinement are summarized in Table 3. H atoms were positioned geometrically and constrained to ride on their parent atoms, with C-H = 0.93 Å and N-H = 0.86 Å , and with U iso (H) = 1.2U eq (C,N). The highest residual electron density and the deepest hole were found 0.29 Å and 0.48 Å from atoms N6 and Zn1, respectively.   Part of the crystal packing of the title compound, showing the eight-and twelve-membered rings [symmetry codes (a) Àx + 1, Ày, Àz; (b) Àx + 2, Ày, Àz]. H atoms have been omitted for clarity.

Figure 4
Part of the crystal packing of the title compound with the N-HÁ Á ÁO hydrogen bonds shown as dashed lines (see Table 1  Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009 where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.29 e Å −3 Δρ min = −0.59 e Å −3 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.