Diaquabis(5-carboxy-2-methyl-1H-imidazole-4-carboxylato-κ2 N 3,O 4)cobalt(II) dimethylformamide disolvate

In the title compound, [Co(C6H5N2O4)2(H2O)2]·2C3H7NO, the CoII ion lies on an inversion center and adopts a slightly distorted CoN2O4 octahedral geometry binding two bidentate chelating 5-carboxy-2-methyl-1H-imidazole-4-carboxylate (H2MIDA−) monoanionic ligands and two axial aqua ligands. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link neighboring molecules, generating a two-dimensional framework containing eight-membered H4O4 rings. In addition, the dimethylformamide solvent molecules are hydrogen bonded to the two-dimensional framework via the NH groups of the H2MIDA− ligands.

In the title compound, [Co(C 6 H 5 N 2 O 4 ) 2 (H 2 O) 2 ]Á2C 3 H 7 NO, the Co II ion lies on an inversion center and adopts a slightly distorted CoN 2 O 4 octahedral geometry binding two bidentate chelating 5-carboxy-2-methyl-1H-imidazole-4-carboxylate (H 2 MIDA À ) monoanionic ligands and two axial aqua ligands. In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link neighboring molecules, generating a two-dimensional framework containing eight-membered H 4 O 4 rings. In addition, the dimethylformamide solvent molecules are hydrogen bonded to the two-dimensional framework via the NH groups of the H 2 MIDA À ligands.
The title compound is composed of one Co (II) ion, two mono-deprotonated H 2 MIDA ligands, two aqua ligands and two DMF solvent molecules, Fig 1. The Co (II) cation lies on a crystallographic inversion center and has a distorted octahedral geometry with the basal plane occupied by two carboxylate O atoms and two N atoms from two chelating H 2 MIDAligands.
There are two axial aqua ligands. In the H 2 MIDA ligand, the carboxyl and carboxylate groups form an intramolecular hydrogen bond with an O···O distance of 2.452 (2) Å.
In the crystal packing, each aqua ligand is involved in two intermolecular O-H···O hydrogen bonds with two carboxyl O atoms from two neighboring molecules to genetrate a two-dimensional supramolecular structure (Fig. 2), in which two aqua ligands and two carboxyl O atoms form a H 4 O 4 eight-membered ring. In addition, the DMF solvates are hydrogen-bonded to the two-dimensional framework via the -NH groups of the H 2 MIDAligands.

Experimental
A solution of cobalt perchlorate hexahydrate (73.2 mg, 0.2 mmol) and H 3 MIDA (15.8 mg, 0.1 mmol) in DMF (6 ml) and methanol (1 ml) was stirred for 5 h. After filtering, the filtrate was left for about two months and pink, block-like crystals of the title compound appeared. Yield: 11 mg (38%).

Refinement
The carboxyl and water H atoms were located in a difference Fourier map and refined with U iso =1.5U eq (O). The O-H distances of water were refined with idealized values of 0.85 Å, however, that of carboxyl is refined freely. All other H-atoms were positioned geometrically and refined using a riding model with C-H (methyl) = 0.96 Å, C-H (aldehyde) = 0.93 Å, N-H = 0.86 Å, and U iso = 1.2U eq (C, N).  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq