Synthesis and structure of d-metal complexes with 2,3,5,6-tetraoxo-4- nitropyridine: Crystal structure of Ni(H2O)6(C 5HO6N2)2·2H2O

Crystal hydrates of nickel(II) perchlorate and cobalt(II), copper(II), and zinc(II) chlorides react with ammonium 2,3,5,6-tetraoxo-4-nitropyridinate (NH4)2(C5HO6N2) 2 to produce the M(H2O)6(C5HO 6N2)2·2H2O complexes. The crystal structure of Ni(H2O)6(C5HO 6N2)2·2H2O has been determined by X-ray single-crystal diffraction. In the course of complex formation, complex cations [Ni(H2O)6]2+ are substituted for the ammonium cations in the organic salt, the organic anions are linked with the coordinated water molecules by O⋯H-O hydrogen bonds, and the dimers of 2,3,5,6-tetraoxo-4-nitropyridinate anions are spatially rearranged so that they cease to be charge-transfer complexes as in the initial (NH4)2(C5HO6N2) 2 salt.