CoMn2O4 spinel from a MOF: synthesis, structure and magnetic studies

Abstract

A hydrothermal reaction of Mn(OAc)₂·4H₂O, Co(OAc)₂·4H₂O and 1,2,4 benzenetricarboxylic acid at 220 °C for 24 h gives rise to a mixed metal MOF compound, [CoMn₂{C₆H₃(COO)₃}₂], I. The structure is formed by the connectivity between octahedral CoO₆ and trigonal prism MnO₆ units connected through their vertices forming a Kagome layer, which are pillared by the trimellitate. Magnetic susceptibility studies on the MOF compound indicate a canted anti-ferromagnetic behavior, due to the large antisymmetric DM interaction between the M²⁺ ions (M = Mn, Co). Thermal decomposition studies indicate that the MOF compound forms a tetragonal mixed-metal spinel phase, CoMn₂O₄, with particle sizes in the nano regime at 400 °C. The particle size of the CoMn₂O₄ can be controlled by varying the decomposition temperature of the parent MOF compound. Magnetic studies of the CoMn₂O₄ compound suggests that the coercivity and the ferrimagnetic ordering temperatures are dependent on the particle size.