Synthesis and order–disorder transition in a novel metal formate framework of [(CH3)2NH2]Na0.5Fe0.5(HCOO)3]

Abstract

We report the synthesis, crystal structure, thermal, dielectric, Raman, infrared, and magnetic properties of [(CH₃)₂NH₂][Na_0.5Fe_0.5(HCOO)₃] (DMNaFe), the first metal formate framework templated by organic cations, presenting an ABO₃ perovskite architecture with NaO₆ octahedra as building blocks of the framework. On the basis of Raman and IR data, assignment of the observed modes to respective vibrations of atoms is proposed. We have found that DMNaFe undergoes a structural phase transition at 167 K on cooling. According to the X-ray diffraction, the compound shows R symmetry at 293 K and triclinic P symmetry at 110 K. The DMA⁺ cations are dynamically disordered in the high-temperature phase and the phase transition is associated with ordering of the DMA⁺ cations and distortion of the metal formate framework. The dielectric studies reveal pronounced dielectric dispersion that can be attributed to slow dynamics of the DMA⁺ cations. Based on the low-temperature magnetic studies, this compound is a weak ferromagnet with a critical temperature 8.5 K.