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Comparison of Covalency in the Complexes of Trivalent Actinide and Lanthanide Cations
journal contribution
posted on 2002-07-25, 00:00 authored by Mark P. Jensen, Andrew H. BondThe complexes of trivalent actinide (Am(III) and Cm(III)) and lanthanide (Nd(III) and Sm(III))
cations with bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2,4,4-trimethylpentyl)monothiophosphinic acid,
and bis(2,4,4-trimethylpentyl)dithiophosphinic acid in n-dodecane have been studied by visible absorption
spectroscopy and X-ray absorption fine structure (XAFS) measurements in order to understand the chemical
interactions responsible for the great selectivity the dithiophosphinate ligand exhibits for trivalent actinide
cations in liquid−liquid extraction. Under the conditions studied, each type of ligand displays a different
coordination mode with trivalent f-element cations. The phosphinate ligand coordinates as hydrogen-bonded
dimers, forming M(HL2)3. Both the oxygen and the sulfur donor of the monothiophosphinate ligand can
bind the cations, affording both bidentate and monodentate ligands. The dithiophosphinate ligand forms
neutral bidentate complexes, ML3, with no discernible nitrate or water molecules in the inner coordination
sphere. Comparison of the Cm(III), Nd(III), and Sm(III) XAFS shows that the structure and metal−donor
atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide
and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalent
actinide cations over trivalent lanthanide cations.
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XAFSmonodentate ligandssulfur donorTrivalent Actinideabsorption spectroscopydithiophosphinate ligand exhibitsacidactinide cationswater moleculesligand displaysdithiophosphinate ligand formsML 3trivalent lanthanide cationschemical interactionscoordination modetrivalent lanthanidephosphinate ligand coordinatesbidentate complexesLanthanide Cationstrivalent actinide cationscoordination spheremonothiophosphinate ligandtrivalent actinide
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