Structural studies of lanthanide complexes with new hydrophobic malonamide solvent extraction agents†

Abstract

Two new hydrophobic malonamide ligands butyl-N,N′-dimethyl-N,N′-diphenyl malonamide and ethoxyethyl-N,N′-dimethyl-N,N′-diphenyl malonamide and corresponding lanthanide complexes [Ln(NO₃)₃(L)₂], Ln = Nd or Pr, have been prepared and structurally characterised. The structural studies establish that the alkyl or alkyloxy groups attached to the central carbon atom of the malonamides do not effect the bidentate co-ordination of adjacent carbonyl oxygen atoms. All the metal complexes presented show the lanthanide to be 10-co-ordinate, being bonded to four oxygen atoms of two malonamides and six oxygen atoms of three nitrates. Malonamide ligands with alkyloxy groups have been shown previously to be better extractants for lanthanide(III) and actinide(III) ions than those with just alkyl groups. This solid state evidence seems to suggest that the enhanced extraction performance of ligands with an ether oxygen in the alkyloxy chain is not due to direct co-ordination between the metal ion and the ether oxygen.