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.

Raman spectroscopic studies across the ferroelectric transition in cobalt substituted dimethyl amine manganese formate

“…This inductive effect could in turn elongate the CO bond directly attached to it and make this bond weaker leading to the observed softening. A similar softening of the ν 2 mode has been observed in earlier substitution studies in these MOF systems …”

Polarized IR and Raman spectra of the novel metal-organic framework [CH3CH2NH3][Cd(HCOO)3]

“…It is worth to mention that previous IR and Raman studies of metal formate frameworks have shown that the lattice modes are expected to be below 400 cm -1 , whereas internal modes can be observed in the 500-3500 cm -1 range [5,9,15,[27][28][29][30].…”

Temperature-dependent studies of [(CH3)2NH2][FeIIIMII(HCOO)6] frameworks (MII = Fe and Mg): structural, magnetic, dielectric and phonon properties

“…Figure S2 shows that DMFeMg does not undergo any phase transitions down to 125 K. (DMM) with M=Mg, Ni and DMNaFe, for which the step-like peak exhibited strong dependence on probing frequency also in the low-temperature phase. 9,16,19 At the same time, the bell shape maximum in the imaginary part of dielectric permittivity shifts to lower temperatures with decreasing frequency. Around the phase transition temperature the peak starts to disappear and a new, broad loss peak corresponding to the low-temperature phase appears ( Figure 2c).…”