Poly[tetraaqua(μ6-9,10-dioxo-9,10-dihydroanthracene-1,4,5,8-tetracarboxylato)dimanganese(II)]

The title complex, [Mn2(C18H4O10)(H2O)4]n, was synthesized from manganese(II) chloride tetrahydrate and 9,10-dioxo-9,10-dihydroanthracene-1,4,5,8-tetracarboxylic acid (H4AQTC) in water. The anthraquinone unit is located about a crystallographic center of inversion. Each asymmetric unit therefore contains one MnII atom, two water ligands and one half AQTC4− anion. The MnII atom is coordinated in a distorted octahedral geometry by four O atoms from three AQTC4− ligands and two water O atoms. Two of the carboxylate groups coordinate one MnII atom in a chelating mode, whereas the others each coordinate two MnII atoms. Each AQTC4− tetra-anion therefore coordinates six different MnII ions and, as a result, a three-dimensional coordination polymer is formed. O—H⋯O hydrogen bonds, some of them bifurcated, between water ligands and neighboring water or anthraquinone ligands are observed in the crystal structure.

The title complex, [Mn 2 (C 18 H 4 O 10 )(H 2 O) 4 ] n , was synthesized from manganese(II) chloride tetrahydrate and 9,10-dioxo-9,10-dihydroanthracene-1,4,5,8-tetracarboxylic acid (H 4 AQTC) in water. The anthraquinone unit is located about a crystallographic center of inversion. Each asymmetric unit therefore contains one Mn II atom, two water ligands and one half AQTC 4À anion. The Mn II atom is coordinated in a distorted octahedral geometry by four O atoms from three AQTC 4À ligands and two water O atoms. Two of the carboxylate groups coordinate one Mn II atom in a chelating mode, whereas the others each coordinate two Mn II atoms. Each AQTC 4À tetra-anion therefore coordinates six different Mn II ions and, as a result, a three-dimensional coordination polymer is formed. O-HÁ Á ÁO hydrogen bonds, some of them bifurcated, between water ligands and neighboring water or anthraquinone ligands are observed in the crystal structure.

Comment
Porous solid materials, such as MOFs (metal-organic frameworks) have been widely studied for their potential applications in gas absorption, separation, catalysis and magnetic materials. Explorations of advanced porous materials for these applications are an intense subject of scientific research (Li et al.,1999;Li et al., 2012;Cheng et al., 2010;Hong et al., 2009;Miller & Gatteschi, 2011;Liu et al., 2010.) Herein we report the crystal structure of the title compound.
The molecular structure of (I) is illustrated in Fig. 1., a summary of the observed hydrogen bonds and the corresponding angles are given in Table 1.
Each asymmetric unit therefore contains one manganese(II) atom, two water ligands and one half AQTC 4ligand. The coordination sphere around manganese is distorted octahedral due to the coordination of four O atoms from three AQTC 4ligands and two O atoms from two water molecules. Two of the carboxylate groups coordinate one manganese in a chelating mode whereas the others each coordinate two manganese center. Each AQTC 4therefore coordinates six different manganese ions and as a result a three-dimensional coordination polymer is formed.
The solution was exposed to air for three days leading to the precipitation of brown crystals (yield 10%).

Refinement
All non-hydrogen atoms were refined anisotropically. H atoms of the H 2 O ligands were determined in difference Fourier maps and refined isotropically with distance restraints for O9-H5 and O9-H6 of 0.82 Å. H atoms of AQTC 4ligands calculated in idealized positions with C-H = 0.93 Å and refined as riding atoms, with U iso (H) = 1.2U eq (C).

Figure 2
A view of the crystal structure of the title compound. 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.