SYNTHESIS OF COMPOUND OXIDES OF LANTHANUM AND 3-d METALS (Co, Ni, Cu) AND THEIR HETEROMETALLIC COMPLEXES WITH SUCCINIC ACID AND PYRIDINE

Анотація

The work presents studies on the synthesis of new heterometallic complexes of La(III) and Co(II), Ni(II), Cu(II) with succinic acid and pyridine (Py). Mixed-ligand, heterometallic coordination compounds of the general composition [М₂La₂(C₄Н₄O₄)₅·4Py]·4Н₂О (М^ІІ=Со, Ni, Cu) were obtained. Their thermal properties were studied and the ability of heterocomplexes to form complex oxides was determined. The complexes were characterized using elemental analysis and thermogravimetric method. Assessment of their thermal stability showed that the thermal decomposition of the synthesized heterocomplexes proceeds in stages and has a multistage nature. Their thermolysis proceeds through the stages of elimination of water molecules (100–220°C), then pyridine (185–310°C), which is accompanied by exothermic effects on the DTA curves, and to the complete thermal decomposition of heterometallic coordination compounds. In the temperature range from 260°C to 700°C, intensive decomposition of complexes occurs, due to the destruction of the organic part, which is accompanied by exothermic effects. During the thermolysis of heterocomplexes at 800°C, 900°C, 1000°C, oxide powders were obtained. Their composition was controlled by X-ray phase analysis. Phase identification was carried out by comparing experimental diffraction patterns with the ICDD PDF-2 databases. It is shown that the compounds [М₂La₂(C₄Н₄O₄)₅·4Py]·4Н₂О (M=Co, Cu) decompose at a temperature of 900°С mainly to complex oxides LaСоО₃ and La₂СuО₄ with small impurities of La(OH)₃ and non-stoichiometric cupric oxide Cu_xO, respectively. The thermal destruction of the complex [Ni₂La₂(C₄Н₄O₄)₅·4Py]·4Н2О is accompanied by the formation of the dominant phase of lanthanum nickelates La₂NiО₄ and LaNiO₃, and a small content of NiO and La(OH)₃ oxides as side phases was also found. Thus, the heterometallic complexes Co₂La₂(C₄Н₄O₄)₅·4Py]·4Н₂О, [Ni₂La₂(C₄Н₄O₄)₅·4Py]·4Н₂О and  [Cu₂La₂(C₄Н₄O₄)₅·4Py]·4Н₂Оcan be used as precursors to obtain complex oxides – cobaltate, nickelate, or lanthanum cuprate with lower energy costs than in solid-phase synthesis.