(μ-Ethane-1,1,2,2-tetracarboxylato)bis[tetraaquamanganese(II)]

In the centrosymmetric title molecule, [Mn2(C6H2O8)(H2O)8], the MnII atom is in an octahedral environment coordinated by six O-atom donors from water molecules and ethane-1,1,2,2-tetracarboxylate ligands. The crystal structure features a three-dimensional hydrogen-bonding network based on a strong and distinctive pattern of O—H⋯O hydrogen-bonding interactions.

In the centrosymmetric title molecule, [Mn 2 (C 6 H 2 O 8 )(H 2 O) 8 ], the Mn II atom is in an octahedral environment coordinated by six O-atom donors from water molecules and ethane-1,1,2,2tetracarboxylate ligands. The crystal structure features a three-dimensional hydrogen-bonding network based on a strong and distinctive pattern of O-HÁ Á ÁO hydrogen-bonding interactions.

Comment
The design and synthesis of metal-organic frameworks(MOFs) has become a very interesting research field. This not only stems from their potential application as functional materials but also from their intriguing structural topologies (Chen et al., 2007;Fan & Zhu, 2006;Li & Yang, 2006). However, frankly speaking, the designed synthesis of coordination networks and supramolecular architectures is still a difficult challenge. The formation of coordination polymers is not only influenced by the geometrical and electronic properties of metal ions but also relying on other factors such as the rigidity or flexibility of the ligands and diversity of metal ions and organic ligands in coordination and noncovalent interactions such as hydrogen bonding (Kim & Jung, 2000;Forster et al., 2002). Therefore, the rational design and construction of coordination polymers based upon assembly of metal ions and multifunctional organic ligands is an interesting research field. Herein we report the crystal structure of the title compound (I).
The molecular structure of (I) is illustrated in Fig. 1., where selected bond distances and bond angles are given in Table 1.
Single-crystal X-ray analysis reveals that 1 crystallizes in the triclinic space group P-1, The structure of 1 is a single molecule in which the asymmetric unit contains one Mn atom, half tce anion, four coordinated water molecules. In complex 1, there is one kind of crystallographically independent Mn II center.1 features a 3-D hydrogen bonding network based on a strong and distinctive pattern of hydrogen bonding interactions. As show in Fig. 2., a one-dimensional chain is formed by bond generated by coordinated water molecule and uncoordinated oxygen atom of ligand tce, Further, one-dimensional chains are linked by bonds to form two-dimensional layers, and two-dimensional layers are also jointed by hydrogen bonds to give rise to three-dimensional structure.

Experimental
A H 2 O solution (10 ml) of sodium 1,1,2,2-tetracarboxyl-ethylene (29.4 mg, 1 mmol) was added to a CH 3 OH solution (10 ml) of Mn(OAc) 2 2.5H 2 O (17.3 mg,1 mmol). The pH of the mixture was adjusted to about 7. The mixture was stirred for 2 h and then filtered.Single crystals appeared after the filtered solution was allowed to stand at room temperature for 2 days.

Refinement
The C-bound H atoms were placed to the bonded parent atoms in geometrically idealized positions (C-H = 0.93, and 0.98 Å) and refined as riding atoms, with U iso (H) = 1.2U eq (C). The O-bound H atoms were located in difference Fourier maps and refined as riding in their as-found relative positions(O-H =0.96 Å) with U iso (H) = 1.5U eq (C).