Mono- and heterocomplexes of Co(II), Nd(III) with oxalic acid and phenanthroline: synthesis, structure and thermal decomposition

Abstract

This work presents the results of studies aimed at determining the conditions for the synthesis of a new heterometallic complex of Co(II) and Nd(III) with oxalic acid in the presence of 1,10-phenanthroline, studying its composition, structure, thermal properties and its ability to form complex oxides. The hetero- and monocomplexes [Сo(C2O4)Phen]24Н2О, [Nd2(C2O4)32Phen], [Сo2Nd2(C2O4)52Phen]4Н2О (Phen – phenanthroline) were synthesized. The complexes were investigated by the following physicochemical research methods: elemental analysis, differential thermal analysis, IR- and diffuse reflection electronic spectroscopies, and X-ray powder diffraction. Based on the analysis of electronic and IR spectra, it was shown that ions of metals bind bidentately with ions of oxalates and with molecules of 1,10-phenanthroline. The structures of the ion of cobalt and ion of neodymium correspond to the distorted octahedron. The ions of metals are bound together by oxalate ligands. The powders of oxides were prepared by thermolysis of the heterocomplex up to 8000C and 10000C. The composition of the obtained oxide powders was controlled by X-ray powder diffraction. When the heterocomplex is heated to 8000C, in addition to the complex oxide NdCoO3, we obtained the following oxides: Nd2O3 (hexagonal crystal system), Nd2O3 (cubic crystal system) and Co3O4 (cubic crystal system). After heating to 10000C, a more pure complex oxide NdCoO3 was obtained. Neodymium cobaltate NdCoO3 crystallizes in the cubic crystal system, the unit cell parameter is a=3.770 Å, the cell volume is 53.568 Å3. The average crystallite size was calculated using the Scherrer formula, and it is equal to ~35 nm. The synthesized heterometallic complex [Сo2Nd2(C2O4)52Phen]4Н2О can be used as a precursor for the preparation of cobaltate of neodymium with lower energy consumption than in solid-phase synthesis.