Rare-earth chelate vapour
Mani Bhaumik1965, Journal of Inorganic and Nuclear Chemistry
MOST rarc4mrth chutes decompose on melting and arc dimout to obtain in the vapour plume, c') In an attempt to obtain volatile ~ chum, me wu made of fluorhmmi lig~ since substitution of fluorinine is known to redu~ in~moiezular forem. This search led to several fluorinated ~-diketone che~tes which sublime without prolnl~w d~mlxzlflion at temperatut~ near 100°C. Studies with europium hexafluoroacety~te (EuHFA) are described here. On heating EuHFA at 120°C under vacuum, it is obllaTed that the sublknate shows a europium fluor~cmce as strong as the starting material. Such a strong fluoregence is characteristic only of a chelated species and, the~ore, the chelate should have passed through thz vapour phase without decompmition. Had the ligands completely separated from the europium ion during the vapour plume, the metal ion would not have sublimed because of a low vapour Wesma~. Also, once the chelate completely decomposes, it is unlikely that a chelated species will be formed again. Attempts were made to measu'.e the chelate vapour pressure. Ordinary electrical gauges could not be used because of difficulties in calib~tion of this vapour, and also because the chelates possibly decompme in these gauges. An alternative technique was employed, making use of the high absorption metBzinnt of the chelates. Molecular substanzes like chelates retain their absorption characteristics well in going from one phase of matter to the other. Since the absorption codtkient of the chelate is accurately known in solutions, the vapour pressure can be computed from a knowledge of the absorption in the vapour phase. Since the operating pressures are low, the perfect gas laws can be applied to a good approximation in computation. The a~ of the chdate wpour was mmmured photoelectrically in a double beam apparatus. The tmmmim~n at 300 m~ (the ~orption peak in the vapc~u" phase) was reduced to 40 per cent at 90°C in a length of 30 ¢m. Taking the molar peak abe~rption ~t of EuHFA in ethanol solution to be 50,000, one estimates the vapour pre~ure at 90°C to be about 7/~. Sublimatinm were ~ out near 12&C where the pre~ures were higher. The EuI-IFA was prepared by an aqueous method. D~lied hexaffhtoroacetylacetone and an equivalent amount of ammonium hydroxide dissolved in water were mixed with an aqueom Eotation of europium chloride. The precipitated products were filtered, washed with water to retnove ammonium chloride, and recrystallized from a mixture of ether and hexane to yield EuHFA with melting point of 181-182°C. Chemical analysis gave the percentages of C, H, and Eu to be 22.2, 1-4, and 19.7, respectively; therefore, the compound is characterized as europium trlshexafluoroacetylacetonate dihydrate. Details of the vapour-pressure, temperature relations and the thermal stability of the chelate vapour are being studied. Volatilities of other fluorinated chelates are also being investigated. Gas chromatographic analysis of the chelate vapours are contemplated.
