Vibrational spectra of mono, di and trimethyl ammonium double sulphates of rare earths Pr, Nd, Ho and Eu

Infrared and Raman spectra of four rare earth (Ho, Eu, Nd and Pr) double sulphates have been recorded and analysed based on the vibrations of methyl ammonium cations, sulphate anions and water molecules. Formation of hydrogen bonds of the type NH⋯O and OH⋯O are identified in all the compounds. Bifurcated hydrogen bonds are present in the compounds with dimethyl ammonium cations. The sulphate anions are distorted and occupy a lower site symmetry in the compounds. The bands obtained for (CH3)2NH2 and SO42− ions indicate that the structural bonding of (CH3)2NH2Eu(SO4)2·H2O and (CH3)2NH2Ho(SO4)2·4H2O is identical. Electronic transition bands of Eu3+ and Nd3+ observed in the Raman spectra of these two compounds have been identified and discussed.