Molten Calcium Nitrate Tetrahydrate: Spectroscopy of Chromium(III), Cobalt(II), Nickel(II) and Copper(II) Nitrates and Some Complexes of Nickel(II) and Cobalt(III)

Abstract

The hydrated nitrates of chromium(III), cobalt(II), nickel(II) and copper(II) dissolved in molten calcium nitrate tetrahydrate at 43°C to form clear coloured solutions. Their spectra, between 30000 and 11000 cm^-1, showed maxima closely similar in wavenumber to those of the corresponding aqueous solutions, and indicated similar octahedral coordination by oxygen from the ligands. However, slightly higher molar absorption coefficients of the metal cations in the molten solutions than those of the aqueous solutions suggested the possibility of mixed coordination by both aqua and nitrato groups. Nickel(II) complexes were rapidly solvolysed in the melt but cobalt(III) displayed more varied behaviour, intriguingly different from those of their aqueous solutions.