engleski

From 3D polymeric heterometallic oxalate-based complexes with magnetic ordering to the spinel oxides

Metal–organic coordination polymers may exhibit a variety of specific properties including porosity, conductivity or luminescence and have potential applications in various fields from heterogeneous catalysis, gas storage and separation to supramolecular magnetism. Due to the diversity of metal species and ligands, coordination geometry, guests inside the pores, and supramolecular arrangements, vastly coordination polymers with various structures and pores have been synthesized and characterized. Since their discovery, oxalate-based extended networks of a general formula [MaII/IIIMbI/II(C2O4)]2n−/n− have attracted a lot of attention because the anionic networks provide magnetic ordering and are able to host a wide variety of functional cations, leading to a rational synthesis of magnetic multifunctional materials. The possibility of using coordination polymers through the thermal decomposition process as molecular precursors in the synthesis of nanomaterials has been considered only recently. This method of obtaining oxide materials, compared with conventional methods, has several advantages. The C2O42− group easily decomposes to gaseous CO2 and CO at low temperatures, and hence, heterometallic oxalate complexes have already been used for the single-step preparation of mixed metal oxides.[1] As a continuation of our magneto-structural studies concerning the polynuclear transition-metal complexes, heterometallic 3D oxalate-bridged polymers {; ; ; ; [A(bpy)3][M2(C2O4)3]·H2O}; ; ; ; n (A = Co2+ or Cu2+ ; M = Mn2+ or Fe2+ ; bpy = 2, 2′-bipyridine) have been prepared and, in addition to the single-crystal X-ray study, characterized by magnetization measurements. Utilizing the preparation of the oxide materials via thermal decomposition, these polymers have been tested as molecular precursors for the formation of spinel oxides CoMn2O4, CuMn2O4 and CuFe2O4. This conversion was explored by thermal analysis, powder X-ray diffraction and magnetic susceptibility measurement. The changes in preparation conditions, namely, temperature of the heat treatment, cause thermally induced cation redistribution within the spinel lattice and an increase of the particle sizes, acting ultimately on the magnetic behavior of the prepared oxides.

coordination polymers ; magnetic order ; molecular precursor ; thermal decomposition ; mixed-metal oxide

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