Screening of the Structure of Americium Extractants Based on a 2,2’-Bipyridyl Scaffold: a Simple Way to a N2,O2-Tetradentate Ligands Library for Rational Design of An/Ln Extractantsстатья
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Аннотация:A library of N-ethylanilides of 2,2’-bipyridine-6,6’-dicarboxylic
acids were synthesized to evaluate the influence of the side
chains on the extraction properties. The structure of the various
diamides is studied in solid state by X-ray and in solution by
2DNMR. In the solid-state, the diamides featured flat Cs
geometry irrespective of the nature and position of the
substituents. Carboxylic groups in the crystals shifted from the
residing planes of both pyridine and aromatic anilide rings
indicating disruption of the conjugated system. The solution
behaviour is substituent dependent. Only three types of
relative orientations of amidic fragments and pyridine rings
were found in solutions of diamides depending on the nature
of the amidic side chain substituents. The conformations of the
diamides mostly depended on the size of the substituent and
less on their electronic properties. Solubility of the diamides
and their metal extraction properties in relation to americium
and europium ions were studied the diamides, bearing
substituents in pyridine rings and in phenyl ring of diamide
moiety (one or two alkyl-, alkoxy-, fluorine-, carboxylic-groups).
The symmetrical substitution in the pyridine moiety critically
diminished both solubility and metal extraction. Metal ions
recovery strongly depended on the substitution in the anilidic
moiety; distribution coefficients depended more on the spatial
arrangement of the substituents and to a lesser extent on their
electronic properties.