Diaquabis(5-bromo-2-hydroxybenzoato)bis(N-methylnicotinamide)zinc(II)

The title mononuclear complex molecule, [Zn(C7H4BrO3)2(C7H8N2O)2(H2O)2], has a crystallographically imposed centre of symmetry. The zinc(II) atom is coordinated by two N atoms from two N-methylnicotinamide ligands, two O atoms from two 5-bromosalicylate anions and two aqua O atoms in a slightly distorted octahedral geometry. Intramolecular O—H⋯O hydrogen-bonding interactions are present. In the crystal structure, molecules are linked by intermolecular O—H⋯O and N—H⋯O hydrogen bonds, forming a two-dimensional network perpendicular to [100].


Comment
The complexes of carboxylic acids with metals, e.g. zinc, are interesting due to different coordination modes of a carboxylate group bound to a metal ion. It is well documented that heterocyclic compounds, especially N-donor ligand systems, play a significant role in many biological systems, being a component of several vitamins and drugs (Nagar, 1990;Cavagiolio et al., 2000). As a part of our ongoing studies of zinc(II) carboxylates (Györyová et al., 2005;Györyová et al., 2006;Bujdošová et al., 2009) we have been exploring the synthesis and crystal structure of zinc(II) 5-bromosalicylate containing N-methylnicotinamide, shown at in vitro study to be a potent anti-inflammatory agent (Gebicki et al., 2003). gen bonding interactions involving the hydroxyl groups and carboxylate oxygen atoms (O3-H1O3···O2) and the equatorially coordinated water molecule and carboxylate oxygen atom (O5-H2O5···O2) stabilize the molecular structure (Fig. 2). Intramolecular hydrogen bonds also influences the orientation and delocalized character of carboxylate group. The molecules of the title compound are linked into a two-dimensional network perpendicular to [100] by intermolecular O5-H1O5···O4 and N2-H1N2···O3 hydrogen bonds (Fig. 3).

Experimental
Analytical reagent grade chemicals were used for the preparation of the title compound. The synthesis was carried out by reaction of aqueous solutions (20 ml) of ZnCl 2 (0.14 g, 1 mmol) and NaHCO 3 (0.17 g, 2 mmol). After complete removal of chloride anions, an acetone solution (10 ml) of 5-bromosalicylic acid (0.44 g, 2 mmol) was added. The resulting solution of sup-2 (5-BrC 6 H 3 -2-(OH)COO) 2 Zn (0.50 g, 1 mmol) was mixed with an aqueous solution (10 ml) of N-methylnicotinamide (0.27 g, 2 mmol). The reaction mixture was stirred for 2 h and left aside for crystallization at room temperature. After two days, a small amount of colourless bright crystals appeared. The resulting crystals were isolated by filtration.

Refinement
The hydrogen atoms of the water molecule were located in difference Fourier map and refined with the O-H distances constrained to 0.82 Å and with U iso (H) = 1.5U eq (O). The H atom bound to N2 was located in a difference Fourier map and refined U iso (H) = 1.2U eq (N). All other H atoms were positioned geometrically and constrained to ride on their parent atoms, with O-H = 0.82 Å, C-H = 0.93-0.96 Å, and with U iso (H) = 1.2U eq (C) or 1.5U eq (C, O) for methyl and hydroxyl H atoms. Fig. 1. The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Symmetry code: (i) 1-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 > σ(F 2 ) is used only for calculating Rfactors(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.