Poly[[hexaaquasesqui(μ-benzene-1,2,4,5-tetracarboxylato)dicopper(II)disodium] monohydrate]

In the title compound, {[Cu2Na2(C10H2O8)1.5(H2O)6]·H2O}n, the Cu2+ ion is hexacoordinated by five O atoms from benzene-1,2,4,5-tetracarboxylate (btec4−) ligands and one water molecule. The Na+ ion is also hexacoordinated, by four O atoms from btec4− ligands and two water molecules. One of the two btec4− molecules sits on a crystallographic inversion centre. CuO6 and NaO6 octahedra are connected, forming bi-dimensional layers. These layers, which extend parallel to the ac plane, are further interconnected by μ10- or μ11-bridging btec4− ligands and by O—H⋯O hydrogen bonds, involving both btec4− ligands and water molecules, forming a three-dimensional network.

In the title compound, {[Cu 2 Na 2 (C 10 H 2 O 8 ) 1.5 (H 2 O) 6 ]ÁH 2 O} n , the Cu 2+ ion is hexacoordinated by five O atoms from benzene-1,2,4,5-tetracarboxylate (btec 4À ) ligands and one water molecule. The Na + ion is also hexacoordinated, by four O atoms from btec 4À ligands and two water molecules. One of the two btec 4À molecules sits on a crystallographic inversion centre. CuO 6 and NaO 6 octahedra are connected, forming bidimensional layers. These layers, which extend parallel to the ac plane, are further interconnected by 10 -or 11 -bridging btec 4À ligands and by O-HÁ Á ÁO hydrogen bonds, involving both btec 4À ligands and water molecules, forming a threedimensional network.

Comment
In recent years, much attention has been paid to coordination polymers that involve covalent bonds or supramolecular contacts. A huge number of novel compounds with interesting crystal structures and topologies have been reported. As  (2007)]. In order to enrich this family of compounds, we recently undertook a study devoted to reactions of H 4 btec with metal ions in gel media. In particular, we were interested in such reactions with agaragar gel bridges in U-shaped tubes, and we have successfully synthesized a novel polymeric complex from H 4 btec and copper (II) chloride. We report here the synthesis and the crystal structure of the title coordination polymer. As shown in Fig. 1, the asymmetric unit of the title compound contains two Cu(II) ions, two Na(I) ions, coordinated water molecules and three btec 4ligands. One of the two crystallographically distinct btec 4ligands is located on an inversion centre. One btec 4ligand acts as a m 10 -bridge that links six Cu(II) ions and four Na(I) ions, while the other acts as a m 11 -bridge that links five Cu(II) ions and six Na(I) ions. Cu(II) ions are hexa-coordinated by five O atoms from four btec 4ligands and one O atom from a water molecule, while Na(I) ions are hexa-coordinated by four O atoms from four btec 4ligands and two O atoms from two water molecules. As shown in Fig. 2, two-dimensional Cu-O-Na layers extend parallel to the ac plane. Furthermore, these two-dimensional layers are interconnected by m 10 -or m 11 -bridging btec 4ligands and by O-H···O hydrogen bonds, forming a three-dimensional framework.

Experimental
All reagents were used as obtained without further purification. Copper (II) chloride was purchased from STREM Chemicals. 1,2,4,5-benzenetetracarboxylic acid was purchased from Acros Organics. Its sodium salt was prepared by addition of four equivalents of sodium hydroxide to a suspension of 1,2,4,5-benzenetetracarboxylic acid in de-ionized water until complete dissolution. Then, the solution was evaporated to dryness. The solid phase was then put in suspension in ethanol, stirred and refluxed for 1 h. After filtration and drying in a desiccator, a white powder of tetrasodium 1,2,4,5-benzene-tetra-carboxylate was obtained (yield = 90%). Single crystals of the coordination polymer were

Refinement
The H-atoms from water molecules that could be found in difference maps were included with constrained coordinates.
Some hydrogen atoms could not be reliably located, so these have only been taken into account in the formula (i.e. not in the model).

Figure 2
A view of the three-dimensional network of the title compound, projected perpendicular to the bc-plane.