Electronic spectra and stability of cobalt halide complexes in molten calcium nitrate tetrahydrate

The complex formation between cobalt(II) and chloride and bromide ions in molten calcium nitrate tetrahydrate at different temperatures has been studied by a spectrophotometric technique. Addition of halide ions to cobalt(H) nitrate solution in calcium nitrate tetrahydrate caused a pronounced shift of the absorption maximum toward lower energies and a large increase of absorption intensity, indicating a change from octahedral to a tetrahedral co-ordination. The change of co-ordination depends on temperature and halide concentration. Stability constants for the [Co(NO3)(4)](2-), [Co(NO3)(2)X-2](2-) and [COX4](2-) complexes at 40 and 70 degreesC and the corresponding species spectra are reported.