Synthesis and order–disorder transition in a novel metal formate framework of [(CH₃)₂NH₂]Na_0.5Fe_0.5(HCOO)₃]

Abstract

We report the synthesis, crystal structure, thermal, dielectric, Raman, infrared, and magnetic properties of [(CH3)2NH2][Na(0.5)Fe(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 R3[combining macron] symmetry at 293 K and triclinic P1[combining macron] 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.