CoCl+: Unique in all of molten saltdom?

The UV-vis spectra of CoCl2 dissolved in molten NaCl-AlCl3 solutions were o btained as a function of composition from slightly basic compositions to fa irly acidic compositions, and the solubility of CoCl2 was determined using both an analytical technique and an electromotive force (EMF) technique. Th e cell used for the EMF measurements was Co/CoCl2-NaAlCl4//NaAlC4-(AgCl)(N) /AgCl (s)Ag, where the mole fraction, N, is fixed. Saturation at 175 degree s C was detected when [delta E/delta N(CoCl2)](T) = 0. A very sharp minimum in the solubility was found in the vicinity of the 50.00 pet NaCl-50.00 pe t AlCl3 composition, and a distinct spectrum with three broad peaks belongi ng to neither tetrahedrally nor octahedrally coordinated Co++ was obtained in this composition region. In this composition region, the solution can be described in terms of five cobalt-containing species of the form CoCln2-n, where n = 0 --> 4, indicating that the solubility of CoCl2 in the NaAlCl4 melt is related to the formation of chlorometallic species that are present in much higher concentration than Co++ ions with no bound Cl- ions, but wh ich are solvated with AlCl4- ions. In the composition range where a unique three-peaked spectrum was observed, the dominant species is the CoCl+ ion. The other significant species could be the neutral CoCl2 molecule. All of t he other cobalt-containing species are present at such low concentrations t hat their spectra do not appear. We think that the asymmetric CoCl+ species is responsible for the observed spectrum because it is present in much hig her concentration than any other species, and it is a stronger absorber of light in the UV-vis region of the spectrum than is the CoCl2. As far as we can discern, this is the only completely asymmetric species that has been i dentified spectroscopically as existing in an inorganic molten salt solutio n.