Poly[μ3-aqua-aqua(μ3-3,5-dinitrobenzoato-κO 1:O 3:O 5)caesium]

In the structure of the title complex, [Cs(C7H3N2O6)(H2O)2]n, the Cs salt of 3,5-dinitrobenzoic acid, the metal complex centres have have irregular CsO8 coordination, comprising two water molecules (one triply bridging and the other monodentate) and four O-atom donors from two nitro groups and one bridging carboxylate O-atom donor from the ligand. Intra-unit O—H⋯O hydrogen-bonding interactions involving both water molecules are observed in the three-dimensional polymeric complex structure.

In the structure of the title complex, [Cs(C 7 H 3 N 2 O 6 )(H 2 O) 2 ] n , the Cs salt of 3,5-dinitrobenzoic acid, the metal complex centres have have irregular CsO 8 coordination, comprising two water molecules (one triply bridging and the other monodentate) and four O-atom donors from two nitro groups and one bridging carboxylate O-atom donor from the ligand. Intra-unit O-HÁ Á ÁO hydrogen-bonding interactions involving both water molecules are observed in the threedimensional polymeric complex structure.

S1. Comment
3,5-Dinitrobenzoic acid (DNBA) has been a popular ligand used alone or in mixed-ligand applications for metal complexation and the structures of a large number of its complexes have been reported. With the alkali metals the structures of the complex salts with Li and Na (Yang & Ng, 2007;Jones et al., 2005): the complex salt adduct with Na (Tiekink et al., 1990;Madej et al., 2007) and the Rb complex salt and salt adduct (Miao & Fan, 2011;Miao et al., 2011) are known but the structure of the Cs complex salt has not been reported. In the structure of the title compound the CsO 8 complex unit ( Fig. 1) is irregular 8-coordinate [Cs-O range, 3.087 (2)-3.346 (2) Å] (Table 1), comprising two water molecules (one triply bridging, the other monodentate) and four O-donors from two nitro groups and one bridging carboxyl-O donor group from the ligand. In the three-dimensional polymeric complex structure (Fig. 2), the rings of the DNBA ligands layer down the short b axis of the unit cell with a ring centroid separation of 4.6223 (1) Å (the b cell dimension) (Fig. 3). Present also are intra-polymer O-H···O hydrogen-bonding interactions involving both water molecules (Table 2).

S2. Experimental
The title compound was synthesized by heating together under reflux for 10 minutes, 0.5 mmol of caesium hydroxide and 0.5 mmol of 3,5-dinitrobenzoic acid in 20 ml of 10% ethanol-water. Room temperature evaporation of the solution to incipient dryness gave yellow needle crystals of the title complex from which a specimen was cleaved for the X-ray analysis.

S3. Refinement
Hydrogen atoms of the coordinated water molecules were located in a difference-Fourier synthesis and both positional and isotropic displacement parameters were allowed to refine. Other H-atoms were included at calculated positions and were allowed to ride, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C).

Figure 1
The molecular configuration and atom-numbering scheme for the title compound, with non-H atoms drawn as 50% probability ellipsoids. For symmetry codes: see Table 1.

Figure 2
A section of the three-dimensional coordination polymer showing inter-unit Cs···Cs associations and 30% probability ellipsoids.

Figure 3
The packing in the unit cell viewed down the the b axial direction showing intra-unit hydrogen-bonding associations as dashed lines. Non-interactive H atoms are omitted. For symmetry codes, see Fig. 1 and Table 2. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.47 e Å −3 Δρ min = −0.56 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