A 3D Oxalate-Based Network as a Precursor for the CoMn₂O₄ Spinel: Synthesis and Structural and Magnetic Studies

Abstract

A novel heterometallic oxalate-based compound of the formula {[Co(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2'-bipyridine) was synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), and magnetization measurement. The molecular structure of 1 is made of a three-dimensional (3D) anionic network, [Mn2(C2O4)3]n(2n-), and tris-chelated cations [Co(bpy)3](2+) occupying the vacancies of the framework. Splitting between the zero-field-cooled (ZFC) and field-cooled (FC) branches of susceptibility below the small peak at 13 K indicates magnetic ordering. Compound 1 was used as a single-source precursor for the formation of the mixed-metal oxide CoMn2O4. This conversion via thermal decomposition was explored by thermal analysis (TGA and DTA), IR spectroscopy, powder XRD, and magnetic susceptibility measurement. From refined structural parameters, it could be seen that the spinel obtained by the thermal treatment of 1 at 800 °C is characterized by the inversion parameter δ = 21%, and therefore the structural formula at room temperature can be written as (tet)[Co(0.79)Mn(0.21)](oct)[Co(0.105)Mn(0.895)]2O4. The temperature dependence of magnetization for CoMn2O4 points to at least three magnetic phases: the ferrimagnetic state is observed below 83 K, and up to 180 K blocking of the magnetic moments of nanocrystallites of 31 nm appears, transforming to paramagnetic-like behavior above 180 K. Microstructural characterization of the CoMn2O4 sample was carried out by means of XRD line-broadening analysis.

3D oxalate-based coordination polymers: Relationship between structure, magnetism and color, studied by high-field ESR spectroscopy

“…The magnetic ground state of the studied compounds could be described as an AFM network of slightly canted Mn(II) spins with the contribution of sample [10,11]. The magnetic ordering in these Mn(II) networks was studied by magnetic susceptibility [39,16,10,11], Mössbauer spectroscopy [39] and neutron diffraction [14] measurements but yet is not well understood.…”

“…The magnetic ordering in these Mn(II) networks was studied by magnetic susceptibility [39,16,10,11], Mössbauer spectroscopy [39] and neutron diffraction [14] measurements but yet is not well understood. The weak…”

“…[10,33] 3.3. X-band ESR spectroscopy X-band ESR spectroscopy has not revealed any significant difference between CuMn2-Green and CuMn2-Red complexes and therefore the results are 180 presented in SI.…”

“…[3,4,5,6,7,8] Oxalate-based CPs have drawn considerable attention in the field of molecule- and a bulky counterion, which templates the dimensionality of these networks and could add a second physical property of interest. [10,11,12,13] A special position have new materials that combine magnetism and luminis- 20 cence, due to desire to control magnetic phase transition of molecule-based magnetic compounds under optical stimuli. [14] Besides searching for multifunctional materials and their applications in optoelectronics, luminescent molecule-based 2 magnets are interesting also with respect to the fundamental understanding of magnetism.…”

Crystallization and Structure Determination of Fac-Triammin-Aquo-Oxalato-Cobalt (III)-Nitrate Monohydrate

“…Oxalato complexes of di-and trivalent cobalt are of significant current interest because of their unusual magnetic properties [1][2][3][4][5][6][7] and as components of metal-organic frameworks [8,9] and 3D coordination networks [10,11]. The oxalato ligand also played a prominent role in the very beginning of OPEN ACCESS transition metal coordination chemistry.…”