Poly[μ-aqua-μ5-[2-(2,3,6-trichlorophenyl)acetato]-caesium]

In the structure of the title complex, [Cs(C8H4Cl3O2)(H2O)]n, the caesium salt of the commercial herbicide fenac [(2,3,6-trichlorophenyl)acetic acid], the irregular eight-coordination about Cs+ comprises a bidentate O:Cl-chelate interaction involving a carboxylate-O atom and an ortho-related ring-substituted Cl atom, which is also bridging, a triple-bridging carboxylate-O atom and a bridging water molecule. A two-dimensional polymer is generated, lying parallel to (100), within which there are water–carboxylate O—H⋯O hydrogen-bonding interactions.

In the structure of the title complex, [Cs(C 8 H 4 Cl 3 O 2 )(H 2 O)] n , the caesium salt of the commercial herbicide fenac [(2,3,6trichlorophenyl)acetic acid], the irregular eight-coordination about Cs + comprises a bidentate O:Cl-chelate interaction involving a carboxylate-O atom and an ortho-related ringsubstituted Cl atom, which is also bridging, a triple-bridging carboxylate-O atom and a bridging water molecule. A twodimensional polymer is generated, lying parallel to (100), within which there are water-carboxylate O-HÁ Á ÁO hydrogen-bonding interactions.

Comment
(2,3,6-Trichlorophenyl)acetic acid (fenac) is a commercial herbicide (O′Neil, 2001) and its crystal structure (White et al., 1979) represents the only entry for this compound in the crystallographic literature. My interest in aromatic carboxylic acid herbicides and in polymeric coordination structures of the alkali metal complexes led to the preparation of the title compound, [Cs(C 8 H 4 Cl 3 O 2 )(H 2 O)] n , from the reaction of fenac with caesium hydroxide in aqueous ethanol, and the structure is reported herein.
In the crystal structure of the title complex, a polymer with a sheet structure is generated which lies parallel to (100) (Fig. 3), and within which there are water O-H···O carboxylate hydrogen-bonding interactions (Table 2).

Experimental
The title compound was synthesized by heating together under reflux for 10 minutes, 0.5 mmol of (2,3,6-trichlorophenyl)acetic acid and 0.5 mmol of CsOH in 15 ml of 10% ethanol-water. Partial room temperature evaporation of the solution gave thin colourless crystal plates of the title complex from which a specimen was cleaved for the X-ray analysis.

Refinement
Carbon-bound hydrogen atoms were placed in calculated positions [aromatic C-H = 0.93 Å and methylene C-H = 0.97 Å] and allowed to ride in the refinement, with U iso (H) = 1.2U eq (C). Hydrogen atoms of the coordinating water molecule were located in a difference-Fourier synthesis but were subsequently allowed to ride, with U iso (H) = 1.5U eq (O). A large maximum residual electron density peak was present (2.176 e -Å -3 ) located at 0.82 Å from Cs1. A short O1W···O1W ii non-bonding contact [2.804 (8) Å] across an inversion centre was also found.

Figure 1
The molecular configuration and atom-numbering scheme for the title compound, with non-H atoms drawn as 40% probability displacement ellipsoids. [For symmetry codes, see Table 1  A partial expansion of the Cs + coordination in the polymer generated by cyclic links through carboxylate, chlorine and water bridges. Ligand H-atoms are omitted. [For symmetry code (vi): -x + 2, y + 1/2, -z + 3/2. For other codes, see Fig. 1 and  The packing of the sheet structure in the unit cell viewed down b. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 2.18 e Å −3 Δρ min = −1.86 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.

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