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)center dot 6.76H(2)O, 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 (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 center dot center dot center dot 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 center dot center dot center dot O hydrogen bonds between the same ligands connect neighboring pillars, thus delineating channels that accommodate the chargebalancing 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 center dot center dot center dot O and O center dot center dot center dot O distances indicate hydrogen bonds of medium strength.