Crystal structure of di­ammonium bis­[tris­(oxamide dioxime-κ(2) N,N′)nickel(II)] bis­[tris­(oxalato-κ(2) O,O′)chromate(III)] 6.76-hydrate

The asymmetric unit of the title compound, (NH(4))(2)[Ni(C(2)H(6)N(4)O(2))(3)](2)[Cr(C(2)O(4))(3)](2)·6.76H(2)O, comprises two NH(4) (+) cations, two [Ni(C(2)H(6)N(4)O(2))(3)](2+) cations and two [Cr(C(2)O(4))(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 (Ni(II) and Cr(III)) 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 NH(4) (+) 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.