Poly[μ3-aqua-aqua-μ5-(4-nitrobenzoato)-caesium]

In the structure of the title complex, [Cs(C7H4NO2)(H2O)2]n, the caesium salt of 4-nitrobenzoic acid, the irregular CsO9 coordination sphere comprises three bridging nitro O-atom donors, a bidentate carboxylate O,O′-chelate interaction, a triple-bridging water molecule and a monodentate water molecule. A three-dimensional framework polymer is generated, within which there are water–carboxylate O—H⋯O and water–water O—H⋯O hydrogen-bonding interactions.

In the structure of the title complex, [Cs(C 7 H 4 NO 2 )(H 2 O) 2 ] n , the caesium salt of 4-nitrobenzoic acid, the irregular CsO 9 coordination sphere comprises three bridging nitro O-atom donors, a bidentate carboxylate O,O 0 -chelate interaction, a triple-bridging water molecule and a monodentate water molecule. A three-dimensional framework polymer is generated, within which there are water-carboxylate O-HÁ Á ÁO and water-water O-HÁ Á ÁO hydrogen-bonding interactions.

Comment
4-Nitrobenzoic acid (PNBA) has proved to be a useful ligand for the preparation of metal complexes, which are mainly monomeric but rarely involve the nitro group in coordination. With the known alkali metal salts of PNBA, the sodium salt (a trihydrate) (Turowska-Tyrk et al., 1988) and the potassium salt (a 1:1 salt-acid adduct) (Srivastava & Speakman, 1961), coordination polymeric structures are formed, but the structures of the rubidium and caesium salts have not been reported. The reaction of 4-nitrobenzoic acid with caesium hydroxide in aqueous ethanol afforded good crystals of the title Cs complex, [Cs(C 7 H 4 NO 2 )(H 2 O) 2 ] n and the structure is reported herein.
In this structure ( Table 1). The bridging extensions in the two-dimensional sheet substructures which extend along the (0 0 1) plane include a centrosymmetric water-carboxyl quadruple cage ( Fig. 2) (Cs···Cs iii = 4.2610 (6) Å] [for symmetry code (iii), see Table 2]. The p-related carboxyl and nitro substituent groups of the PNBA ligand link the sheets across c, and generate an overall a three-dimensional coordination polymer (Fig. 3). This type of structure extension through the p-related benzoate carboxyl and nitro functional groups is similar to that found in other alkali metal complexes with the 4-nitroanthranilate salts of sodium (a dihydrate) and potassium (a monohydrate) (Smith, 2013), and caesium (a monohydrate) (Smith & Wermuth, 2011).

Experimental
The title compound was synthesized by heating together for 10 minutes, 0.5 mmol of 4-nitrobenzoic acid and 0.5 mmol of CsOH in 15 ml of 10% ethanol-water. Partial room temperature evaporation of the solution gave colourless elongated 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 [C-H = 0.95 Å] and allowed to ride in the refinement, with U iso (H) = 1.2U eq (C). Hydrogen atoms of the coordinated water molecule were located in a difference Fourier map but were subsequently allowed to ride, with U iso (H) = 1.5U eq (O).

Figure 1
The molecular configuration and atom-numbering scheme for the coordination polyhedron of title complex, with non-H atoms drawn as 40% probability displacement ellipsoids. For symmetry codes: see Table 1.

Figure 2
A partial expansion of the CsO 9 coordination sphere in the polymeric structure. For symmetry codes: (vii) x + 1, y, z; (viii) -x, -y, -z + 1. For other symmetry codes, see Fig. 1   The packing of the structure in the unit cell viewed along a. Hydrogen-bonding associations are shown as dashed lines.

Poly[µ 3 -aqua-aqua-µ 5 -(4-nitrobenzoato)-caesium]
Crystal data 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 )