The infrared spectra of (NH4)2M″(SO4)2.6H2O has been analysed in the region 4000–250 cm−1. The dynamics of each crystal has been discussed in terms of 234 phonon modes, including 3 acoustical ones, using the unit cell approximation. The ambiguity in the assignments of the bands in the region 900–500 cm−1 has been removed by assigning the bands in this region to the libratory modes of H2O molecules. It has been concluded that the NH4+ and SO42− ions have a symmetry lower thanTdand also the complex [M″(H2O)6]2+ has a symmetry lower than Oh. The hydrogen bonding is the strongest in the Ni-salt and the weakest in the Mg-salt.
Volume 94, 2020
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