catena-Poly[[diaquacobalt(II)]-μ-4,4′-[1,4-phenylenebis(oxy)]dibutanoato-κ4 O,O′:O′′,O′′′]

In the title coordination polymer, [Co(C14H16O6)(H2O)2]n, the CoII ion, situated on a twofold rotation axis, is coordinated by four O atoms from two 4,4′-[1,4-phenylenebis(oxy)]dibutanoate (L) ligands and two water molecules in a highly distorted octahedral geometry. Each L ligand is situated on an inversion center and bridges two CoII atoms, forming a zigzag polymeric chain propagating in [10]. Intermolecular O—H⋯O hydrogen bonds further consolidate the crystal packing.

In the title coordination polymer, [Co(C 14 H 16 O 6 )(H 2 O) 2 ] n , the Co II ion, situated on a twofold rotation axis, is coordinated by four O atoms from two 4,4 0 -[1,4-phenylenebis(oxy)]dibutanoate (L) ligands and two water molecules in a highly distorted octahedral geometry. Each L ligand is situated on an inversion center and bridges two Co II atoms, forming a zigzag polymeric chain propagating in [101]. Intermolecular O-HÁ Á ÁO hydrogen bonds further consolidate the crystal packing.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CV5012).

Comment
Benzene-1,4-dioxydiacetic acid is an important biologically active compound commonly used in herbicides and plantgrowth agents. Two phenoxyacetate groups have versatile bonding modes to metal ions and easily forms complexes (Dai et al., 2009;Zhu et al., 2008;Li et al., 2010). Benzene-1,4-dioxydibutanoic acid is an interesting dicarboxylate ligand. To our knowledge, there have been no reports about its coordination compounds. Recently, we obtained the title cobalt polymer (I), and its crystal structure is reported here.
In the structure of (I), each cobalt(II) atom is coordinated by four oxygen atoms from two benzene-1,4-dioxydibutyrate ligands and two water molecules, displaing highly distorted octahedral geometry ( Fig. 1). Each ligand situated on an inversion center bridges two cobalt(II) centers to form polymeric zigzag chain propagated in direction [10-1] (Fig. 2). Intermolecular O-H···O hydrogen bonds (Table 1) consolidate further the crystal packing.

Experimental
The ligand was prepared according to the literature method (Zhang et al., 2009). A mixture of CoSO4 (0.5 mmol), benzene-1,4-dioxydiacetic acid (0.5 mmol), NaOH (1 mmol) and H 2 O (12 ml) was placed in a 23 ml Teflon reactor, which was heated at 423 K for three days and then cooled to room temperature. Single crystals were obtained after washing with water and drying in air.

Refinement
All H atoms were placed in idealized positions (O-H = 0.85 Å and C-H = 0.93-0.97 Å) and refined as riding atoms with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (O). Fig. 1. A portion of the crystal structure of (I) showing the atomic labeling and 30% probability displacement ellopsoids [symmetry codes: (A) -x, y, -z + 3/2; (B) -x + 1/2, -y + 5/2, -z + 1].  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.