Diaquabis(4-methoxybenzoato-κO)bis(nicotinamide-κN 1)nickel(II) dihydrate

In the mononuclear title compound, [Ni(C8H7O3)2(C6H6N2O)2(H2O)2]·2H2O, the NiII ion is located on a crystallographic inversion center. The asymmetric unit further contains one 4-methoxybenzoate anion, one nicotinamide (NA) ligand and one coordinated and one uncoordinated water molecule; all ligands are monodentate. The four O atoms in the equatorial plane around the NiII ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two pyridine N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxylate group and the attached benzene ring is 7.2 (1)°, while the pyridine and benzene rings are oriented at a dihedral angle of 72.80 (4)°. An intramolecular O—H⋯O hydrogen bond links the uncoordinated water molecule to one of the carboxylate 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.

In the mononuclear title compound, [Ni(C 8 H 7 O 3 ) 2 (C 6 H 6-N 2 O) 2 (H 2 O) 2 ]Á2H 2 O, the Ni II ion is located on a crystallographic inversion center. The asymmetric unit further contains one 4-methoxybenzoate anion, one nicotinamide (NA) ligand and one coordinated and one uncoordinated water molecule; all ligands are monodentate. The four O atoms in the equatorial plane around the Ni II ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two pyridine N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxylate group and the attached benzene ring is 7.2 (1) , while the pyridine and benzene rings are oriented at a dihedral angle of 72.80 (4) . An intramolecular O-HÁ Á ÁO hydrogen bond links the uncoordinated water molecule to one of the carboxylate groups. In the crystal structure, intermolecular O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network.

Comment
As a part of our ongoing investigation on 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 title compound, (I), is a mononuclear complex, where the Ni II ion is located on a crystallographic inversion center. The asymmetric unit contains one 4-methoxybenzoate (PMOB) anion, one nicotinamide (NA) ligand and one coordinated and one uncoordinated water molecules, all ligands are monodentate ( Fig.   1). The crystal structures of some NA and/or DENA complexes of Cu II , Co II , Ni II , Mn II and Zn II ions, [Cu(C 7 H 5 O 2 ) 2 (C 10 H 14 N 2 O) 2 ], (II) (Hökelek et al., 1996), [Co(C 6 (Table 1), and the Ni II ion is displaced out of the least-squares plane of the carboxylate group (O1/C1/O2) by 0.7794 (1) Å. The dihedral angle between the planar carboxylate group and the benzene ring A (C2-C7) is 7.2 (1)°, while that between rings A and B (N1/C9-C13) is 72.80 (4)°. An intramolecular O-H···O hydrogen bond (Table 2) links the uncoordinated water molecule to one of the carboxylate groups ( Fig. 1).
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.

Experimental
The title compound was prepared by the reaction of NiSO 4 .6H 2 O (2.63 g, 10 mmol) in H 2 O (50 ml) and nicotinamide (2.44 g, 20 mmol) in H 2 O (50 ml) with sodium 4-methoybenzoate (3.48 g, 20 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving blue single crystals.
supplementary materials sup-2 Refinement Atoms H21, H22 (for NH 2 ) and H51, H52, H61, H62 (for H 2 O) were located in a difference Fourier map and refined isotropically. The remaining H atoms were positioned geometrically with C-H = 0.95 and 0.98 Å for aromatic and methyl H atoms and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for aromatic H atoms. Fig. 1. The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Primed atoms are generated by the symmetry operator: (') 2 -x, 1 -y, 1 -z. Dashed lines indicate the hydrogen-bonding.