Raman spectroscopic and spectroelectrochemical studies in molten sodium chloroaluminates

Two Raman spectrometer systems have been assembled and are described in this work; a spectrograph designed for use with a photodiode array detector and a computer controlled double monochromator equipped with a photomultiplier. The suitability of the spectrometers for use in molten salt investigations is discussed.

Raman cells suitable for spectroscopic and spectroelectrochemical investigations in molten salts have been constructed and applied to several chemical systems.

Raman spectra of WCl₆, WOCl₄, WCl₅, WCl₄, K₃W₄Cl₉, and WCl₂, as solids and in acidic melts, been obtained using visible and ultraviolet laser excitation. Spectra of WCl₄, K₃W₂Cl₉, and WCl₂ in acidic melts show no features that may be used to identify solute species.

The ultraviolet Raman spectroelectrochemical behavior of chloranil in basic and acidic sodium chloroaluminates has been studied. Spectroscopic results indicate that, in acidic melts, chloranil exists as an adduct with the solvent (e. g. AI₂Cl₇^-) coordinated at one of the carbonyl oxygens and at the carbon-carbon double bonds. The reversible two-electron exchange in basic melts was followed by observing the disappearance and reappearance of neutral chloranil Raman features. The reduction of chloranil in acidic melts takes place as two one-electron exchanges; the redox behavior of complexed chloranil and complexed radical anion was observed. No spectral evidence was obtained for the complexed dianion in basic or acidic melts.