Diaquabis(4-methylbenzoato-κO)zinc(II)

The Zn atom in the title mononuclear complex, [Zn(C8H7O2)2(H2O)2], lies on a special position of site symmetry 2. The carboxylate group binds in a monodentate manner so that the geometry is best described as tetrahedral. Adjacent molecules are linked by O—H⋯O hydrogen bonds into a three-dimensional network.

The Zn atom in the title mononuclear complex, [Zn(C 8 H 7 O 2 ) 2 (H 2 O) 2 ], lies on a special position of site symmetry 2. The carboxylate group binds in a monodentate manner so that the geometry is best described as tetrahedral. Adjacent molecules are linked by O-HÁ Á ÁO hydrogen bonds into a three-dimensional network.

Related literature
For related literature, see: Song et al. (2007).

S1. Comment
In the structural investigation of 4-methylbenzate complexes, it has been found that the 4-methylbenzoic acid functions as a multidentate ligand [(Song et al. (2007)], with versatile binding and coordination modes. In this paper, we report the crystal structure of the title compound, (I), a new Zn complex obtained by the reaction of 4-methylbenzoic acid with zinc chloride in alkaline aqueous solution.
As illustrated in Figure 1, the Zn II atom, possesses crystallogarphically imposed C 2 symmetry, which is coordinated by two O atoms from two 4-methylbenzate ligands and two water molecules, and displays a tetrahedral geometry.
Intermolecular O-H···O hydrogen bonding interactions (Table 1) between the coordinated water molecules and the carboxyl O atoms of 4-methylbenzate ligands stabilize the structural packing (Fig. 2).

S2. Experimental
A mixture of zinc nitrate(1 mmol), 4-methylbenzoic acid (1 mmol) NaOH (1.5 mmol) and H 2 O (12 ml) was placed in a 23 ml Teflon reactor, which was heated to 433 K for three days and then cooled to room temperature at a rate of 10 K h -1 .
The crystals obtained were washed with water and dryed in air.

S3. Refinement
Carbon-bound H atoms were placed at calculated positions and were treated as riding on the parent C atoms with C-H = 0.93 -0.97 Å, and with U iso (H) = 1.2 U eq (C). Water H atoms were tentatively located in difference Fourier maps and were refined with distance restraints of O-H = 0.82 Å and H···H = 1.29 Å, each within a standard deviation of 0.01 Å, and with

Figure 1
The structure of (I), showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids. Unlabeled atoms are related to the labelled atoms by the symmetry operator (-x, y, 0.5 -z). 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 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.