Poly[[bis{μ2-1,2-bis[(1H-imidazol-1-yl)methyl]benzene}(μ4-9,10-dioxo-9,10-dihydroanthracene-1,4,5,8-tetracarboxylato)dicobalt(II)] dihydrate]

The title complex, {[Co2(C18H4O10)(C14H14N4)2]·2H2O}n was synthesized from CoCl2·6H2O, 9,10-dioxo-9,10-dihydroanthracene-1,4,5,8-tetracarboxylic acid (H4AQTC) and 1,2-bis[(1H-imidazol-1-yl)methyl]benzene (o-bix) in water. The anthraquinone unit is located about a crystallographic center of inversion. Each asymmetric unit therefore contains one CoII atom and one o-bix ligand, as well as half an AQTC4− ligand and an additional solvent water molecule. The CoII ions are tetrahedrally surrounded by two O atoms from two AQTC4− anions and by two N atoms from two o-bix ligands, forming a two-dimensional coordination polymer. The solvent water molecules are connected to the carboxylate groups by O—H⋯O hydrogen bonds. Additional weak C—H⋯O hydrogen bonds are observed in the crystal structure.


Related literature
For general background to metal organic frameworks, see: Li et al. (1999Li et al. ( , 2012
The center of the anthraquinone moiety is a crystallographic center of inversion. Each asymmetric unit therefore contains one cobalt atom and one o-bix ligand as well as one half AQTC 4ligand and an additional solvent water molecule. Cobalt(II) ions are tetrahedrally surrounded by two O atoms from two AQTC 4and two N atoms from two obix ligands forming a 2D-coordination polymer.

Experimental
A mixture of H 4 AQTC (0.025 mmol, 9.8 mg) and o-bix (0.025 mmol, 6.0 mg) were added to distilled water (4 ml) and ultra-sounded for 10 min. The pH value of the mixture was then adjusted to 8.0 with NaOH (0.5 mol.L -1 ). Then CoCl 2 × 6 H 2 O (0.05 mmol, 12 mg) was added. The reactants were placed in a Teflon-lined stainless steel vessel, heated for 3 days, and then cooled to ambient temperature over 12 h. Red block shaped crystals of (I) were obtained in 30% yield.

Refinement
All non-hydrogen atoms were refined anisotropically. H atoms of the H 2 O were located from difference Fourier maps and refined isotropically with a distance restraint of O-H = 0.83-0.99Å. Carbon bound H atoms were placed in calculated positionswith C-H = 0.93 Å for aromatic and 0.97 Å for methylene hydrogen atoms and refined as riding atoms, with U iso (H) = 1.2U eq (C).

Figure 2
A view of stacking structure of the title compound (H atom omited for clear except solvent water).   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 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.