Crystal structure of poly[μ2-aqua-aqua-(μ2-4-nitro-2,5,6-trioxo-1,2,5,6-tetra-hydro-pyridin-3-olato)hemi-μ4-oxalato-barium(II)]

Hexa-aqua-nickel(II) bis-[tri-aqua-μ3-oxalato-di-μ-oxalato-bariumchromate(III)] tetra-hydrate

The structure of the title compound is made up of corrugated anionic layers of formula [BaCr(C₂O₄)₃(H₂O)₃]_n^n– that leave voids accommodating the charge-compensating cations, [Ni(H₂O)₆]²⁺ (point group symmetry ), as well as the water mol­ecules of crystallization.

The title compound, [Ni(H₂O)₆][BaCr(C₂O₄)₃(H₂O)₃]₂·4H₂O, was obtained in the form of single crystals from the slow evaporation of an aqueous mixture of {Ba₆(H₂O)₁₇[Cr(C₂O₄)₃]₄}·7H₂O and NiSO₄·6H₂O in the molar ratio 1:4. Its structure is made up of corrugated anionic (101) layers of formula [BaCr(C₂O₄)₃(H₂O)₃]_nⁿ⁻ that leave voids accommodating the charge-compensating cations, [Ni(H₂O)₆]²⁺ (point group symmetry ), as well as the water mol­ecules of crystallization. The anionic layers are built from the connection of barium and chromium atoms through bridging oxalate ligands. The Cr^III atom is hexa­coordinated by O atoms of three oxalate ligands while the Ba^II atom is tenfold coordinated by three O atoms of water mol­ecules and seven O atoms of four oxalate ligands. Each Ni^II atom sits on an inversion center and is coordinated by six water mol­ecules. One of the uncoordinated water mol­ecules is disordered over two sites, with a refined occupancy ratio of 0.51 (5):0.49 (5). In the crystal, extensive O—H⋯O hydrogen-bonding inter­actions link the anionic layers, the charge-balancing cations as well as the water mol­ecules of crystallization into a three-dimensional supra­molecular network.