Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 4-amino-1,2,4-triazolidine-3,5-dione (urazine)

The complexing capability of urazine as neutral (Hur) or monoanionic (ur) ligand towards divalent cations (Co, Ni, Cu, Zn) was examined. Complexes CoCl2(Hur)2·4H2O (1), NiCl2(Hur)2·4H2O (2) and Zn(SO4)(Hur)·2H2O (3), in which urazine acts as neutral ligand, were synthesized and characterized. It is worth noting that in the examined crystal the chiral complex 3 shows only the A enantiomer due to a spontaneous resolution. Complexes Co(ur)2·4H2O (4), NiCl(ur)·H2O (5), CuCl(ur)·2H2O (6) and Zn(ur)2·2H2O (7), in which coordinated deprotonated urazine molecules are present, were synthesized in aqueous solution starting from the urazine sodium salt. Other copper(II) complexes Cu3(NO3)2(ur)4·6H2O (8), Cu(ur)2·4H2O (9), Cu2(SO4)(ur)2·2H2O (10) were synthesized in aqueous solution starting from the free ligand. The crystal structures of 1, 3, 8, 9, 10 were determined by X-ray diffraction methods. In the structurally characterized complexes Hur acts only as N,O chelating agent in 1 and 3, whereas ur acts as monodentate through the deprotonated triazolidine nitrogen atom in 9, tridentate in 8 and tetradentate in 8 and 10.