Poly[di-μ-aqua-diaqua-di-μ6-malonato-cobalt(II)dipotassium(I)]

In the title complex, [CoK2(C3H2O4)2(H2O)4]n, the Co atom is located on a position with site symmetry 2/m, the K atom and one water molecule are located on a mirror plane, and the malonate and one water molecule are located on a twofold rotation axis. The KI atom is seven-coordinated by four carboxylate O atoms from four malonate ligands and by three water O atoms, forming a distorted polyhedron. The CoII atom is in an almost octahedral environment formed by four carboxylate O atoms from two malonate ligands and two water O atoms. The structure consists of layers parallel to (20) built up from edge-sharing KO7 and CoO6 polyhedra, which are connected by O—H⋯O hydrogen bonding including water molecules into a three-dimensional network.

In the title complex, [CoK 2 (C 3 H 2 O 4 ) 2 (H 2 O) 4 ] n , the Co atom is located on a position with site symmetry 2/m, the K atom and one water molecule are located on a mirror plane, and the malonate and one water molecule are located on a twofold rotation axis. The K I atom is seven-coordinated by four carboxylate O atoms from four malonate ligands and by three water O atoms, forming a distorted polyhedron. The Co II atom is in an almost octahedral environment formed by four carboxylate O atoms from two malonate ligands and two water O atoms. The structure consists of layers parallel to (201) built up from edge-sharing KO 7 and CoO 6 polyhedra, which are connected by O-HÁ Á ÁO hydrogen bonding including water molecules into a three-dimensional network.
Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97. These values agree with those found in literature (Baggio et al., 2003;Li et al.). The apical coordination position are occupied by oxygen atoms from water mlecules with bond length [Co-O 2.1347 (18) Å] and an angle value of 180.00 (11) (Zhao et al., 2007). The potassium cation has an O7 donor set made up by four µ 2 -bridging malonate oxygen atoms and one µ 2 -bridging water oxygen atoms and two water coordinated molecules. The K cations share four oxygen atoms bridges from malonate groups and two oxygen atoms from water molecule with Co cations. There are hydrogen bonds between water molecules and carbonyl groups of the malonate anions. The cations Co II and K I are arranged in the following sequence: Co-K-K-Co. The metal atoms are found at linear positions [K-Co-K, 180.00 (0)°] as shown in Fig. 2. The Co-K distance is 3.5726 (13) Å. Two K atoms are found to be very close together, having a distance of 4.2086 (14) Å, which is a short metal-metal distance for these types of complexes. The insertion of two polyhedra of KO 7 between two polyhedra of CoO 6 results in long Co-Co distances. These two types of geometries form zigzag layers parallel to the ac-plane and alternating with malonate groups along the b axis.
The water oxygen atoms provide bridges between K cations. The different polyhedra are still bound to each other through edge-sharing with a compact layer structure defining narrow crossed channels.

Experimental
In a round bottomed flask, cobalt acetate tetrahydrate (0.4982 g, 2 mmol) dissoveld in a mixture of water and methanol (10 ml, 1:1) was introduced. Imidazole (0.2720 g, 4 mmol) dissolved in 10 ml of the same mixture was added. The solution turn pink. After 10 mn of stirring, 10 ml of a mixture of methanol and water (10 ml, 1:1) containing malonic acid (0.2081 g, 2 mmol) and KOH (0.2240 g, 4 mmol) was added to the pink solution. After 2 h under stirring, the suspension was filtered off and the precipitate was washed with water and diethyl ether before dring under P 2 O 5 . The compound was recrystallized in a mixture of water and dimethylformamide (1/1). After one week, suitable pink crystals for X-ray analyses was obtained.

Refinement
The H atoms of the water molecules were located in a Fourier difference map and freely refined. H atoms of the CH 2 groups were geometrically placed and refined with a riding model with U iso (H) = 1.2 U eq (C).  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.