Diaquabis(4-bromobenzoato-κO)bis(nicotinamide-κN 1)copper(II)

The asymmetric unit of the title mononuclear CuII complex, [Cu(C7H4BrO2)2(C6H6N2O)2(H2O)2], contains one half-molecule, the CuII atom being located on an inversion center. The unit cell contains two nicotinamide (NA), two 4-bromobenzoate (PBB) ligands and two coordinated water molecules. The four O atoms in the equatorial plane around the CuII ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxylate group and the adjacent benzene ring is 22.17 (16)°, while the pyridine ring and the benzene ring are oriented at a dihedral angle of 82.80 (6)°. In the crystal, N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. A weak C—H⋯π interaction is also observed.

The asymmetric unit of the title mononuclear Cu II complex, [Cu(C 7 H 4 BrO 2 ) 2 (C 6 H 6 N 2 O) 2 (H 2 O) 2 ], contains one half-molecule, the Cu II atom being located on an inversion center. The unit cell contains two nicotinamide (NA), two 4-bromobenzoate (PBB) ligands and two coordinated water molecules. The four O atoms in the equatorial plane around the Cu II ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxylate group and the adjacent benzene ring is 22.17 (16) , while the pyridine ring and the benzene ring are oriented at a dihedral angle of 82.80 (6) . In the crystal, N-HÁ Á ÁO, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into a threedimensional network. A weak C-HÁ Á Á interaction is also observed.

Experimental
Cg is the centroid of the N1/C8-C12 pyridine ring.

Comment
As a part of our ongoing investigations of 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 asymmetric unit of the title mononuclear Cu II complex, (Fig. 1 (16) Å (for water oxygens), and the Cu-N bond length is 2.0116 (16) Å, close to standard values (Allen et al., 1987). The Cu atom is displaced out of the mean-plane of the carboxylate group (O1/C1/O2) by -0.5279 (1)  In the crystal, intermolecular N-H···O, O-H···O and C-H···O hydrogen bonds link the molecules into a three-dimensional network (Table 1). There also exists a weak C-H···π interaction (Table 1).

Experimental
The title  Atoms H21 and H22 (for NH 2 ) and H41 and H42 (for H 2 O) were located in a difference Fourier map and were freely refined.
The C-bound H-atoms were positioned geometrically with C-H = 0.95 Å for aromatic H-atoms, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq