Diaquabis(cyclohexanecarboxylato)zinc(II) monohydrate

In the title compound, [Zn(C7H11O2)2(H2O)2]·H2O, the ZnII atom (site symmetry ) is four-coordinated by two O atoms from the cyclohexanecarboxylate anions and two O atoms from the water molecules, forming a slightly distorted square-planar coordination. The O atom of the uncoordinated water molecule lies on a crysatllographic twofold rotation axis. In the crystal, the components are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, [Zn(C 7 H 11 O 2 ) 2 (H 2 O) 2 ]ÁH 2 O, the Zn II atom (site symmetry 1) is four-coordinated by two O atoms from the cyclohexanecarboxylate anions and two O atoms from the water molecules, forming a slightly distorted squareplanar coordination. The O atom of the uncoordinated water molecule lies on a crysatllographic twofold rotation axis. In the crystal, the components are linked by O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Comment
There has been much research interest in acid metal complexes due to their molecular architectures and biological activities (e.g. Cheng et al., 2006). In this work, we report here the crystal structure of the title compound, (I). In (I), all bond lengths are within normal ranges (Allen et al., 1987) (Fig. 1). The Zn II atom is four-coordinated by two O atoms from the cyclohexanecarboxylate and two O atoms from the water molecules, forming a slightly distorted square-planar coordination (Table 1). In the crystal, O-H···O hydrogen bonds (Table 2) link the components.

Experimental
A mixture of cyclohexanecarboxylic acid (256 mg, 2 mmol) and ZnNO 3 .6H 2 O (1 mmol, 297 mg) in methanol (10 ml) was stirred for 2 h. After keeping the filtrate in air for 6 d, colourless blocks of (I) were formed.

Refinement
The O-bound H atoms were located in a difference map and their positions were refined with the restraint O-H = 0.82 (1)Å.
The other H atoms were positioned geometrically (C-H = 0.97-0.98Å) and refined as riding, with U iso (H) = 1.2U eq (carrier). Fig. 1. The molecular structure of (I) showing 30% probability displacement ellipsoids. Atoms with the suffix A are generated by the symmetry code (1-x, 1-y, -z).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance mat- 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.  (4) C5-C6 1.513 (6)