MOLTEN LITHIUM NITRATE-POTASSIUM NITRATE EUTECTIC - THE REACTION OF RUTHENIUM(III), RHODIUM(III) AND PALLADIUM(II) CHLORIDES

Ruthenium(III) chloride was oxidised in pure nitrate eutectic at 200-350 °C to dark blue ruthenium(IV) oxide, with some intermediate stabilisation due to formation of chloro-complexes. The oxide was initially somewhat amorphous but became fully crystalline after heating to 600 °C. Rhodium(III) chloride dissolved to give yellow solutions, possibly involving nitrite coordination which gave brown insoluble potassium rhodate(III) (KRhO2) from 300 °C. Additions of potassium chloride gave red solutions, and the increased chloro-complexation resulted in greater stability towards the Lux-Flood acid-base reaction. Palladium(II) chloride also dissolved to give yellow solutions at 200 °C which reacted above 300 ° C. Red solutions of chlore-complexes, formed on addition of potassium chloride, also showed increased stability with respect to that in pure nitrate, reacting only from 400 ° C. In each case the dark brown insoluble product was palladium(II) oxide. The red chloride-containing melts had higher absorbances at 28300 and 22500 cm-1 than pure nitrate melts, indicating the formation of mixed chloro-nitrate complexes, probably octahedral, in the former. © 1990.