Tetraaquabis[4-(methylamino)benzoato-κO]nickel(II)

The title complex, [Ni(C8H8NO2)2(H2O)4], is centrosymmetric with the NiII ion located on a centre of symmetry. It contains two 4-(methylamino)benzoate (PMAB) anions and four coordinated water molecules. 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 two O atoms of the PMAB anions in the axial positions. In the crystal structure, intermolecular O—H⋯O, O—H⋯N, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network.


Comment
The structure-function-coordination relationships of the arylcarboxylate ion in transition metal 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 medium of synthesis Shnulin et al., 1981). Transition metal complexes with biochemical molecules frequently show interesting physical and/or chemical properties, as a result 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 varieties of their coordination modes (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000). The title compound was synthesized and its crystal structure is reported herein.
The title compound is a monomeric complex, with the Ni II ion on a centre of symmetry. It contains two 4-(methylamino)benzoate (PMAB) ligands and four coordinated water molecules. The PMAB ligands are monodentate. The four O atoms (O3, O4, and the symmetry-related atoms O3' and O4') in the equatorial plane around the Ni atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the carboxylate O atoms (O2 and O2') of the symmetry related PMAB ligands ( Fig. 1 and Table 1 (Table 2) link the molecules into a three-dimensional network.

Experimental
The title compound was prepared by the reaction of Ni(SO 4 ).6(H 2 O) (1.31 g, 5 mmol) in H 2 O (50 ml) and sodium 4-(methylamino)benzoate (1.74 g, 10 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving green single crystals.
supplementary materials sup-2 Refinement H atoms of NH group and water molecules were located in difference maps and refined isotropically; the O-H and and H···H distances in the water molecules were restrained to 0.95 (2) Å and 1.46 (4) Å, respectively. The remaining H atoms were positioned geometrically with C-H = 0.93 and 0.96 Å for aromatic and methyl H, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.2 for aromatic H and x = 1.5 for methyl 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. The primed atoms are generated by the symmetry operation (-x, 1 -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.