Comparative studies of vibrational properties and phase transitions in metal-organic frameworks of [NH4][M(HCOO)3] with M = Mg, Zn, Ni, Fe, Mn

• [NH4][M(HCOO)3] M = Ni, Fe, Mn were grown.
• Raman and IR studies of [NH4][M(HCOO)3] were performed.
• IR data confirmed an order–disorder character of the phase transitions.
• Correlations between size and/or mass of divalent cation and wavenumbers were found.
• Splitting and the activation energy for reorientational motions of NH4+ is proportional to Tc.

Room temperature experimental infrared (IR) and Raman spectra of [NH4][M(HCOO)3] compounds with M = Mg, Zn, Ni, Fe, Mn were analyzed in order to propose the assignment of the experimental bands to the respective internal and lattice modes. We also report temperature-dependent IR studies of [NH4][Ni(HCOO)3] and [NH4][Fe(HCOO)3] in the temperature range 5–295 K, and compare them with the previously reported data for the Zn and Mg analogs. The temperature-dependent data provide deeper insight into mechanism of the phase transition and relationship between the phase transition temperature and chemical composition of the studied compounds.