Infrared Study of Water Structure in Salt Hydrates

Infrared spectra are reported for hydrates of zinc nitrate, of potassium thiocyanate, and of mixtures of potassium thiocyanate with thiocyanates of mercury and zinc. These systems were studied over the range of temperatures 90° to −163°C, and with variable water content. Most of these systems were liquid above room temperature, but were studied as solids below room temperature. The broad water absorption bands were seen to split into a number of distinct components on cooling, these components sharpening, changing in frequencies and in intensities as temperature was decreased. The ice structure, shown by systems of high water content, was not present in the low-temperature spectra of systems of low water content containing divalent metal ions. Instead, peaks characteristic of coordinated and variously hydrogen-bonded water molecules were distinguishable. Assignment of these peaks and their temperature dependence is discussed.