Crystal structure of poly[μ2-aqua-aqua(μ<inf>2</inf>-4-nitro-2,5,6-trioxo-1,2,5,6-tetrahydropyridin-3-olato)-hemi-μ<inf>4</inf>-oxalato-barium(II)]

In the title coordination polymer, [Ba(C<inf>5</inf>HN<inf>2</inf>O<inf>6</inf>)(C<inf>2</inf>O<inf>4</inf>)<inf>0.5</inf>(H<inf>2</inf>O)<inf>2</inf>]<inf>n</inf>, the tenfold coordination of the Ba centre consists of four O atoms from the two 4-nitro-2,5,6-trioxo-1,2,5,6-tetrahydropyridin-3-olate (L) anions, three O atoms of two oxalate anions and three water molecules. The Ba - O bond lengths fall in the range 2.698 (3)-2.978 (3) Å. The L ligand chelates two Ba atoms related by a screw axis, leading to formation of fused five- and six-membered chelate rings. Due to the bridging function of the ligands and water molecules, the complex monomers are connected into polymeric two-dimensional layers parallel to the bc plane. Intermolecular O - H⋯O hydrogen bonds link these layers into a three-dimensional supramolecular framework.