Crystal structure of trans-diaquabis(nicotinamide-κN 1)bis(4-nitrobenzoato-κO)manganese(II)

In the title centrosymmetric MnII complex, the MnII atom is coordinated by two 4-nitrobenzoate (NB) anions, two nicotinamide (NA) ligands and two water molecules; the NB and NA ligands act as monodentate ligands. The resulting MnN2O4 coordination polyhedron is a distorted octahedron.


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. The NA ring is the reactive part of nicotinamide adenine dinucleotide (NAD) and its phosphate (NADP), which are the major electron carriers in many biological oxidation-reduction reactions (You et al., 1978). 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 with potential applications in biological systems (Antolini et al., 1982). ISSN 2056-9890 Crystal structures of metal complexes with benzoic acid derivatives have been reported extensively because of the varieties of their coordination modes. For example, Co and Cd complexes with 4-aminobenzoic acid (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000), Co complexes with benzoic acid (Catterick et al., 1974), 4-nitrobenzoic acid  and phthalic acid (Adiwidjaja et al., 1978), and Cu with 4-hydroxybenzoic acid  have been described. Mn complexes closely related to the title compound, diaquabis(4-nitrobenzoato)bis(1H-1,2,4-triazol-3-amine)manganese (Zhang et al., 2013) and diaquabis(1H-imidazole)bis(4-nitrobenzoato)manganese (Xu & Xu, 2004), have also been reported.

Structural commentary
The asymmetric unit of the title mononuclear complex contains one Mn II atom (site symmetry 1), one 4-nitrobenzoate (NB) anion, one nicotinamide (NA) ligand and one water molecule, all ligands coordinating in a monodentate manner. In the complex, the two carboxylate O atoms (O2 and O2 iii ) of the two symmetry-related monodentate NB anions and the two symmetry-related water O atoms (O6 and O6 iii ) around the Mn II atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination sphere is completed by the two pyridine N atoms (N2 and N2 iii ) of the two symmetry-related monodentate NA ligands in the axial positions [symmetry code: (iii) Àx, Ày, Àz; Fig. 1

Synthesis and crystallization
The title compound was prepared by the reaction of The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. Intramolecular O-HÁ Á ÁO hydrogen bonds are shown as dashed lines. Unlabelled atoms are symmetry-related to labelled atoms by (Àx, Ày, Àz). Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A packing diagram of the title compound, viewed down the c axis. Intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds are shown as dashed lines. mide (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 colourless 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.