Spectrophotometric Investigation of Cobalt Chloride Complex Formation in Aqueous Calcium Nitrate–Ammonium Nitrate Melts at T = 328.15 K: Influence of Water Content

Abstract

In this work, the absorption spectra of cobalt(II) nitrate and chloride complexes in the composition xCa(NO3)2–(1 – x)NH4NO3–H2O have been investigated in the 400–800 nm range of wavelength at T = 328.15 K and atmospheric pressure p = 101.3 kPa. Spectra were recorded in 0.3 Ca(NO3)2–0.7 NH4NO3–H2O solutions with variable water content (R = H2O/salt mole ratio; Rws = 1.0, 1.2, 1.6 and 2.0), and in xCa(NO3)2–(1 – x)NH4NO3–H2O (x = 0.3, 0.5 and 0.7) solutions where the H2O/salt mole ratio was kept constant (Rws = 2.0). The blue shift of the absorption maximum with increasing water content (Rws) suggests simultaneous coordination by water molecules and nitrate ions. From an analysis of the spectra, it can be concluded that the following complexes: [Co(NO3)4(H2O)2]2−, [Co(NO3)2Cl2]2− and [CoCl4]2− were formed. The overall stability constants of these complexes and the corresponding resolved species spectra were calculated at T = 328.15 K.