engleski

From oxalate-based heterometallic compounds to nanocrystalline Ca-Cr oxides

The heterobimetallic polymeric compounds {; ; [CaCr2(bpy)2(C2O4)4]•0.83H2O}; ; n (1) and {; ; [CaCr2(phen)2(C2O4)4]•0.33H2O}; ; n (2) (bpy = 2, 2'- bipyridine ; phen = 1, 10-phenanthroline) were synthesized and characterized by spectroscopy, x- ray diffraction and magnetic susceptibility measurements. The crystal structure of 2 is reported: the [Cr(phen)(C2O4)2]− unit, through the two oxalate groups, acts as a chelating ligand towards Ca cations, resulting in one-dimensional (1D) double zigzag chains, formed of diamond- shaped units. The ability of compounds 1 and 2 to act as the single-source precursors for the formation of the Ca–Cr oxides is explored by thermal analysis (TGA and DTA), powder x-ray diffraction and IR spectroscopy. The heat treatment of 1 and 2 resulted in the formation of the mixed-metal oxide phases, CaCrO4, α-CaCr2O4 and β-CaCr2O4. Thermal processing of the compounds at 1100 °C in the stream of air, led to the appearance of the orthorhombic β-CaCr2O4 phase as the major crystalline oxide, together with CaCrO4. By heating the samples up to 1100 °C in the nitrogen flow, only the β-CaCr2O4 phase formed, whereas the heating at 1400 °C caused the crystallization of two polymorphs, α-CaCr2O4 and β-CaCr2O4. Magnetic behaviour of the β-CaCr2O4 phase pointed to the presence of magnetic moments freezing in coexistence with a weak ferromagnetic order.

heterometallic compounds ; Ca-Cr oxide

nije evidentirano