catena-Poly[[cobalt(II)-μ-aqua-μ-propanoato-κ2 O:O′-μ-propanoato-κ2 O:O] monohydrate]

The title compound, {[Co(C2H5COO)2(H2O)]·H2O}n, was synthesized by the reaction of cobalt(II) carbonate hydrate with aqueous propionic acid. The structure consists of polymeric infinite linear chains with composition [Co(C2H5COO)4/2(H2O)2/2]∞ running along [010]. The chains are formed by Co2+ ions linked with bridging propionate groups and water molecules, with a Co⋯Co distance along the chains of 3.2587 (9) Å. The Co2+ ion is six-coordinated in a strongly distorted octahedral geometry. The chains are connected to each other by a network of O—H⋯O hydrogen bonds involving solvent water molecules.

The title compound, {[Co(C 2 H 5 COO) 2 (H 2 O)]ÁH 2 O} n , was synthesized by the reaction of cobalt(II) carbonate hydrate with aqueous propionic acid. The structure consists of polymeric infinite linear chains with composition [Co(C 2 H 5 COO) 4/2 (H 2 O) 2/2 ] 1 running along [010]. The chains are formed by Co 2+ ions linked with bridging propionate groups and water molecules, with a CoÁ Á ÁCo distance along the chains of 3.2587 (9) Å . The Co 2+ ion is six-coordinated in a strongly distorted octahedral geometry. The chains are connected to each other by a network of O-HÁ Á ÁO hydrogen bonds involving solvent water molecules.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FJ2358).

Comment
Cobalt carboxylates are of great importance because of their application in homogeneous oxidation catalysis (Gates, 1992;Parshall & Ittel, 1992;Partenheimer, 1995), and their interesting magnetic properties (Eremenko et al., 2009). Carboxylate ligands coordinated to transition metal ions can adopt different binding modes and form a great number of various cage complexes and a variety of different one-dimensional, two-dimensional and three-dimensional structures.
The title compound, [Co(C 2 H 5 COO) 2 (H 2 O)] n .nH 2 O (I), actually named as cobalt(II) propionate dihydrate, is attracting our attention as the starting substance for the synthesis of mixed-valence cobalt carboxylates. This salt was synthesized and its crystal structure is reported herein.
The crystal structure of (I) contains one symmetrically independent Co 2+ cation coordinated to four O atoms of four bridging propionates and two O atoms of bridging water molecules in a strongly distorted octahedral coordination (Fig. 1).
It is rather interesting that the use of acetic acid instead of propionic acid in the synthesis of (I) result in the formation of monomeric cobalt(II) acetate tetrahydrate (Sobolev et al., 2003), and the polymeric cobalt(II) acetate dihydrate is formed by recrystallization of cobalt(II) acetate tetrahydrate from acetic acid (Jiao et al., 2000).

Experimental
To a solution of propionic acid (7.4 g, 100 mmol) in water (15 ml), an excess of fresh cobalt(II) carbonate hydrate, CoCO 3 .xH 2 O, (8.0 g, approximately 60 mmol) was added. The reaction mixture was stirred for 8 h at room temperature, followed by filtrating the unreacted CoCO 3 .xH 2 O out. The filtrate was allowed to stand at room temperature for slow evaporation. The red single crystals of (I) suitable for X-ray diffraction studies were obtained after several days. Yield 85%.

Refinement
For a single-crystal X-ray diffraction experiment, a red transparent crystal of (I) was mounted on the Bruker Smart APEX II diffractometer. The experiment was performed at 170 K. The structure was solved by the direct method and refined using SHELXL-97 program (Sheldrick, 2008). The positions of hydrogen atoms of water molecules were localized from the supplementary materials sup-2 differential Fourier synthesis and H atoms of the CH 2 and CH 3 groups were calculated by the algorithm incorporated in the SHELXL program complex. Hydrogen atoms kept fixed with U iso (H) = 1.5U eq (C). Fig. 1. [Figure 1. The coordinated mode and linkage of the complex (I). Displacement ellipsoids of non-H atoms are drawn at the 40% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius. Symmetry codes: i = -x + 1/2, y + 1/2,-z + 1/2; ii = -x + 1/2, y-1/ 2, -z + 1/2.] 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 > 2σ(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.