Cobalt(II) chloride complexes in calcium nitrate tetrahydrate melt

In this work a series of spectrophotometric measurements of cobalt(II) chloride in calcium nitrate tetrahydrate melts containing variable amounts of calcium chloride (from 0 to 3.1 mol dm(-3)) were performed at different temperatures from 40 to 70 degrees C. The solutions in pure calcium nitrate tetrahydrate showed octahedral co-ordination, the position of the absorption maximum being at 19420 cm(-1) (512 nm). Addition of chloride caused a shift of the absorption maximum toward lower energies and a large increase of the absorption coefficient indicating a change from octahedral to tetrahedral or distorted octahedral co-ordination, characteristic for cobalt(II) chloride complexes in aqueous nitrate melts. The position of the absorption maximum of the octahedral and tetrahedral complexes and the values of the molar absorption coefficients indicates some co-ordination also by nitrate ion. Stability constants for [Co(NO3)(4)](2-), [Co(NO3)(2)Cl-2](2-) and [CoCl4](2-) and the corresponding resolved species spectra are reported.