Poly[μ-aqua-aqua-μ4-naphthalene-1,8-dicarboxyl-ato-barium]: a layer structure.

The title compound, [Ba(C12H6O4)(H2O)2] n , is represented by a layer-like structure built of BaO8 polyhedra. The asymmetric unit contains a Ba(2+) ion, half a coordinating water mol-ecule and half a μ4-bridging naphthalene-1,8-dicarboxyl-ate (1,8-nap) ligand, the whole structure being generated by twofold rotational symmetry. The carboxyl-ate groups of the 1,8-nap ligands act as bridges linking four Ba(2+) ions, while each Ba(2+) ion is eight-coordinated by O atoms from four 1,8-nap ligands and two coordinating water mol-ecules. In the crystal, there are O-H⋯O hydrogen bonds involving the water mol-ecules and carboxyl-ate O atoms in the BaO8 polyhedra. Each BaO8 polyhedron is connected via corner-sharing water O atoms or edge-sharing ligand O atoms, forming a sheet parallel to the bc plane. These sheets stack along the a-axis direction and are connected via van der Waals forces only. The naphthalene groups protrude above and below the layers of the BaO8 polyhedra and there are voids of ca 208†à (3) bounded by these groups. No residual electron density was found in this region. The crystal studied was twinned by pseudo-merohedry, with a refined twin component ratio of 0.5261†(1):0.4739†(1).