Complexation of Eu(III) with alkyl-substituted malonamides in acetonitrile

The complexation of Eu(III) with a series of alkyl-substituted malonamide ligands was studied in organic solvents using calorimetry, FT-IR and luminescence spectroscopy. The formation constants were determined in acetonitrile containing small amounts of dimethyl sulfoxide. The effects of substitution on the nitrogen atoms as well as on the central carbon atom were evaluated. For the substitution on the nitrogen atoms, the formation constants decrease in the order: N,N,N',N'-tetramethylmalonamide (TMMA) > N,N'-dibutyl-N,N'-dimethylmalonamide (DMDBMA) > N,N,N',N'-tetrahexylmalonamide (THMA) > N,N,N',N'-tetraisopropylmalonamide (TiPMA). For substitution on the central carbon atom, the formation constants decrease in the order: N,N,N',N'-tetrahexyl-2-methylmalonamide (MeTHMA) > N,N,N',N'-tetrahexylmalonamide (THMA) > N,N,N',N'-tetrahexyl-2,2-dimethylmalonamide (DMeTHMA). These orders are discussed in terms of the steric effect and the ligand basicity.