Orotic acid complexes of Co(II), Ni(II), Zn(II) and Cd(II) with imidazoleSyntheses, spectroscopic and thermal studies

The [Co(HOr)(H2O)2(im)2] (1), [Ni(HOr)(H2O)2(im)2] (2), [Zn(H2O)2(im)4](H2Or)2 (3) and [Cd(HOr)(H2O)(im)3] (4) complexes (H3Or: orotic acid, im: imidazole) were synthesized and characterized by elemental analysis, magnetic and conductance measurements, UV-vis and IR spectra. The thermal behaviour of the complexes was also studied by simultaneous thermal analysis techniques (TG, DTG and DTA). The orotate ligand (HOr2−) coordinated to the Co(II), Ni(II) and Cd(II) ions are chelated to the deprotonated pyrimidine nitrogen (N(3)) and the carboxylate oxygen, while do not coordinate to the Zn(II) ion is present as a counter-ion (H2Or−). The first thermal decomposition process of all the complexes is endothermic deaquation. This stage is followed by partially (or completely) decomposition of the imidazole and orotate ligands. In the later stage, the remained organic residue exothermically burns. On the basis of the first DTGmax, the thermal stability of the complexes follows order: 2, 176°C>1, 162°C>4, 155°C>3, 117°C in static air atmosphere. The final decomposition products which identified by IR spectroscopy were the corresponding metal oxides.