Crystal structure of di­ammonium bis­­[tris­­(oxamide dioxime-κ2N,N′)nickel(II)] bis­­[tris­­(oxalato-κ2O,O′)chromate(III)] 6.76-hydrate

The asymmetric unit of the title compound, (NH4)2[Ni(C2H6N4O2)3]2[Cr(C2O4)3]2·6.76H2O, comprises two NH4+ cations, two [Ni(C2H6N4O2)3]2+ cations and two [Cr(C2O4)3]3– anions, as well as eight water mol­ecules of crystallization of which only one is fully occupied. In the cationic and anionic complexes, the central atoms (NiII and CrIII) are each surrounded by three bidentate ligands (N-chelating oxamide dioxime and O-chelating oxalate, respectively), resulting in distorted octa­hedral coordination spheres. In the crystal, O—H⋯O hydrogen bonds between the oxamide dioxime ligands as donor groups and the oxalate ligands as acceptor groups alternately connect the cationic and anionic complexes into infinite pillars extending parallel to [100]. Moreover, N—H⋯O hydrogen bonds between the same ligands connect neighboring pillars, thus delineating channels that accommodate the charge-balancing NH4+ cations as well as the water mol­ecules of crystallization. Although the H atoms could not be localized for these two species, the corresponding N⋯O and O⋯O distances indicate hydrogen bonds of medium strength.