Synthesis, physicochemical, and thermal characterization of coordination compounds of Cu(II) with a pyrazole-type ligand

Abstract

Four new coordination compounds of Cu(II) were synthesized with ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (L) and different co-ligands. In the reaction of warm methanolic solutions of CuX2·nH2O (X = Cl, n = 2; X = Br, n = 0; X = NO3, n = 3) and the ligand in mole ratio 1:2, bis(ligand) complexes Cu(L)2Cl2 (1), Cu(L)2Br2 (2) and Cu(L)2(NO3)2 (3) were obtained. Unlike this, reaction of CuCl2 with the ligand in the presence of LiOAc yielded to the formation of dimeric complex of the formula [Cu(L)(OAc)2]2 (4), with four acetate ions as bridging ligands. In all these complexes, ligand L is coordinated in a monodentate manner through N2 nitrogen atom. The coordination environment in the dimeric complex is octahedral, while in the monomeric complexes the central atom is tetra-coordinated. The molar conductivity data in DMF show that the acetate ions in the dimeric complex are coordinated even in solution. In the monomeric compounds, the molar conductivity data increase in the order 1 < 2 < 3. Since the applicability of the coordination compounds depends on their thermal properties, the thermal decomposition of the complexes was followed by simultaneous TG–DSC measurements. The thermal stability of the monomeric compounds in flowing argon increases in the reverse order as the molar conductivity data. The course of the decomposition is different in the case of the nitrato-compound (3). The decomposition of 3 is followed by a strong exothermic heat effect due to the presence of nitrate ion which is a strong oxidation agent. The decomposition of the other complexes is endothermic, taking place in more or less overlapped reactions. The decomposition of the compounds is completed to 600 °C.