Molten lithium carbonate–sodium carbonate–potassium carbonate eutectic: electronic spectroscopy of first-row transition metal compounds

Abstract

Stable solutions containing chromate(VI), cobalt(II), nickel(II), and copper (III) have been obtained at 420 °C in a molten lithium carbonate–sodium carbonate–potassium carbonate eutectic. Electronic spectroscopy has demonstrated the existence of the tetrahedral chromate(VI) in the melt while nickel(II) and copper(II) exhibited six-fold co-ordination by oxygen, the nickel(II) species appearing to change to a more symmetrical octahedral co-ordination on solidification. The cobalt(II) geometry can be interpreted as octahedral or dodecahedral. While chromate(VI) dissolved readily in the melt without apparent decomposition, attempts to prepare more concentrated solutions (>0.01 mol kg^–1) of the acidic cobalt(II), nickel(II), or copper(II) cations resulted in the precipitation of the respective metal oxide due to acid–base reactions with the carbonate ion.