1D Heterometallic Oxalate Compounds as Precursors for Mixed Ca–Cr Oxides – Synthesis, Structures, and Magnetic Studies

Abstract

AbstractThe heterodimetallic compounds {[CaCr2(L)2(C2O4)4]·xH2O}n [L = 2,2′‐bipyridine (bpy), x = 0.83 (1); L = 1,10‐phenanthroline (phen), x = 0.33 (2)] were synthesized and characterized by IR spectroscopy, X‐ray diffraction and magnetic measurements. The crystal structure of 2 is reported: the chelation of a [Cr(phen)(C2O4)2]– units towards Ca cations results in 1D double zigzag chains. The ability of 1 and 2 to act as single‐source precursors for the formation of Ca–Cr oxides is explored by thermal analysis, powder X‐ray diffraction and IR spectroscopy. The thermal processing of 1 and 2 at 1100 °C in air led to the appearance of the β‐CaCr2O4 phase as the major crystalline oxide. By heating the samples up to 1100 °C in nitrogen, only the β‐CaCr2O4 phase formed, whereas heating at 1400 °C caused the crystallization of two polymorphs, α‐ and β‐CaCr2O4. The magnetic behaviour of β‐CaCr2O4 pointed to the freezing of magnetic moments in coexistence with a weak ferromagnetic order.