Fluorinated β-diketones for the extraction of lanthanide ions:: Photophysical properties and hydration numbers of their EuIII complexes

Tris(beta-diketonato) europium (III) with a series of variably fluorinated ligands derived from 3,5-heptanedione were synthesised with the aim of determining their hydration state under extraction conditions. The number of coordinated water molecules was determined by measuring the lifetime of the Eu(D-5(0)) excited level in water and deuterated water, The hydration gain (Delta q = q - q(0)) after shaking chloroform solutions during 10 min with 0.1 M NaClO4 aqueous solutions depends on the fluorination extent of the diketonates: fluorination of one methyl group leads to a decrease in Delta q of ca. 0.5 unit, while fluorination of one ethyl group results in a decrease of ca. 1.3 units. Highly fluorinated complexes (i.e with hexafluoroacetylacetonate and related ligands) display a hydration number close to one while poorly fluorinated compounds (or nonfluorinated ones, such as the acetylacetonate complex) have a hydration state close to two. Photophysical properties of the Eu-III beta-diketonates are also described and the synthesis of the fluorinated beta-diketones is re-investigated and discussed in details. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).