Room temperature experimental infrared (IR) and Raman spectra of [NH 4 ][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 [NH 4 ][Ni(HCOO) 3 ] and [NH 4 ][Fe(HCOO) 3 ] in the temperature range 5–295K, 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.