Crystal structure of a CoII coordination polymer: catena-poly[[μ-aqua-bis(μ-2-methylpropanoato)-κ2 O:O′;κ2 O:O-cobalt(II)] monohydrate]

The present paper describes the synthesis and crystal structure of a cobalt(II) isobutyrate dihydrate, based on a slightly distorted CoO6 repeat unit comprising four bridging carboxylate O-atom donors and two bridging water donors, giving one-dimensional polymeric chains with composition {[Co{(CH3)2CHCO2}2(H2O)]·H2O}n. Hydrogen bonding through the water molecules gives two-dimensional sheets lying parallel to (100).

In the title cobalt(II) coordination polymer with isobutyrate ligands, {[Co{CH(CH 3 ) 2 CO 2 } 2 (H 2 O)]ÁH 2 O} n , the Co 2+ ion is hexacoordinated in a slightly distorted octahedral coordination environment defined by two O atoms from two bridging water molecules and four O atoms from four bridging carboxylate ligands. The carboxylates adopt two different coordination modes, -( 2 O:O 0 ) and -( 2 O:O), forming a one-dimensional polymeric chain extending along [010]. The intra-chain cobaltÁ Á Ácobalt separation is 3.2029 (2) Å . The polymeric chains are linked by hydrogen bonds involving the water molecules of solvation, giving a two-dimensional network structure lying parallel to (100).

Chemical context
Carboxylate anions still remain a popular choice as bridging ligands because of their ability to form diverse oligo-and polynuclear structures. Oligo-and polynuclear cobalt carboxylates in turn have attracted great attention because of their utilization in homogeneous oxidation catalysis (Gates, 1992;Parshall & Ittel, 1992;Partenheimer, 1995;Ward et al., 2013a), and their interesting magnetic properties (Ward et al., 2013b;Eremenko et al., 2009). Recently, we have reported on the crystal structures of the hydrated polymeric cobalt(II) propionate (Fischer et al., 2010) and butyrate (Fischer et al., 2011), which were prepared by the reaction of cobalt(II) carbonate hydrate with the corresponding aqueous carboxylic acid. The aim of these studies was to investigate the influence of the steric features of the carboxylate anion on the structure of the resulting compounds. Cobalt(II) carboxylates are of interest for our group as starting materials for the synthesis of mixed-valence cobalt carboxylates Fischer, Kuznetsov, Shchukarev & Belyaev, 2012). In addition, we intend to examine the catalytic activity of the cobalt(II) carboxylates obtained, which will be used for introduction into the sodalite cages of synthetic NaY zeolites, modified by decationation and dealuminizing methods.
As a part of our ongoing studies on these compounds, we describe here synthesis and crystal structure of the title compound, {[Co{CH(CH 3 ) 2 CO 2 } 2 (H 2 O)]ÁH 2 O} n , (I).

Structural commentary
The structure of (I) contains one independent Co 2+ cation coordinated by four O atoms from four bridging isobutyrate ligands and two O atoms from two bridging water molecules (O1W) in a distorted octahedral coordination. A water molecule of solvation (O2W) is also present (Fig. 1). The Co-O bond lengths are in the range 2.0142 (6)-2.1777 (6) Å (Table 1) and the cis-angles about the Co 2+ atom vary in the range 78.99 (3)-110.31 (2) . This data correlates with the angles and the distances in cobalt(II) acetate dihydrate which has a similar structure (Jiao et al., 2000), as well as with the closely related cobalt(II) propionate dihydrate (Fischer et al., 2010) and cobalt(II) butyrate 1.7-hydrate (Fischer et al., 2011).
The structure of (I) is based on infinite chains with 1 [Co(H 2 O)((CH 3 ) 2 CHCOO) 2 ] composition, extending along [010] (Fig. 2). The CoÁ Á ÁCo distance within the chain is 3.2029 (2) Å . The formation of polymeric chains may be a plausible reason for the crystal growth being predominantly along the b axis. The bridging carboxylate groups adopt two coordination modes, -  Table 2).

Synthesis and crystallization
The title compound was synthesized using a similar procedure as for the synthesis of the analogous carboxylates cobalt(II) propionate dihydrate (Fischer et al., 2010) and cobalt(II) butyrate 1.7-hydrate (Fischer et al., 2011). To a mixture of isobutyric acid (8.8 g, 100 mmol) and water (100 ml The packing diagram of (I), showing the interactions between the coordination polymer chains. Hydrogen bonds are shown as dashed lines. The carbonbound H atoms are omitted for clarity.

Figure 2
The one-dimensional polymeric structure of (I) extending along [010], with the intramolecular hydrogen bond shown as a dashed line. The carbon-bound H atoms and the water molecule of solvation have been omitted. allowed to stand at room temperature for slow evaporation. Red single crystals of (I) suitable for X-ray diffraction were obtained after several days. The yield was 81%.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms of the water molecules were located from differenc maps and refined in an isotropic approximation with U iso (H) set to 1.5U eq (O). Other hydrogen atoms were placed in calculated positions and refined using a riding model with d(C-H) = 0.98 Å , U iso (H) = 1.2U eq (C) for the tertiary carbon atoms and d(C-H) = 0.96 Å , U iso (H) = 1.5U eq (C) for the methyl groups.

catena-Poly[[µ-aqua-bis(µ-2-methylpropanoato)-κ 2 O:O′;κ 2 O:O-cobalt(II)] monohydrate]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.