Hexaaquacobalt(II) and hexaaquacadmium(II) 4-nitro-2,3,5,6-tetraoxopyridinates [M(H2O)6](C5HN2O6)2 · 2H2O (M = Co and Cd): Synthesis, structures, and properties

The complexes [Cd(H 2 O) 6 ](C 5 HN 2 O 6 ) 2 · 2H 2 O ( I ) and [Co(H 2 O) 6 ](C 5 HN 2 O 6 ) 2 · 2H 2 O ( II ) were obtained in the crystalline state by reactions of cobalt chloride and cadmium chloride with ammonium 4-nitro-2,3,5,6-tetraoxopyridinate, (NH 4 ) 2 · (C 5 HO 6 N 2 ) 2 . Their cocrystallization gave the heterometallic complex [Cd 0.32 Co 0.68 (H 2 O) 6 ](C 5 HN 2 O 6 ) 2 · 2H 2 O ( III ). The crystal and molecular structures of complexes I-III were determined by X-ray diffraction. It was demonstrated that the complexation reactions occur by replacement of two ammonium cations 4-nitro-2,3,5,6-tetraoxopyridinate by the complex cations [M(H 2 O) 6 ] 2+ . The tetraoxopyridinate anions and the complex cations are hydrogen-bonded through the coordinated and crystallization water molecules as well as through the O atoms of the organic anion. The thermolysis of complexes I and II was examined by TGA.