Vibrational Spectra of Molten Salts. II. Infrared Spectra of Some Divalent Metal Nitrates in Alkali-Metal Nitrate Solutions

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Abstract
Infrared spectra of thin films of Mg(NO3)2, Sr(NO3)2, Ba(NO3)2, Cd(NO3)2, and Pb(NO3)2, in molten KNO3 and equimolar KNO3–NaNO3 mixtures have been obtained over the spectral region 4000–200 cm−1. All the nitrates except those of Mg and Cd were in the anhydrous state. Even at temperatures of 300°C or more, the magnesium and cadmium nitrate melts retained small amounts of water. As the concentrations of the divalent metal nitrates were increased, some nitrate bands split, and new low‐frequency lines were observed in some cases. These are located at 380 and 340 cm−1 for Mg(NO3)2 solutions, at 520 cm−1 for Cd(NO3)2, and around 420 cm−1 for Pb(NO3)2. The splitting of the ν3 line of free nitrate decreases in the order Mg2+>Cd2+>Ca2+>Pb2+>Sr2+>Ba2+. Except for Sr2+, this is the order of the ionic potentials. The observed bands are assigned and discussed in terms of complexes formed between metal and nitrate ions. Relative strengths of nitrate and chloride binding by Cd2+ and Mg2+ ions have been investigated by addition of Cl− ion to the mixed nitrate systems.