Synthesis and characterization of mono- and bis-(tetraalkylmalonamide)uranium(VI) complexes

The complex [UO2(NO3)2(TMMA)] (TMMA=N,N,N′,N′-tetramethylmalonamide) was structurally characterized by single-crystal X-ray diffraction. The complex consists of two bidentate nitrate ions and one bidentate TMMA ligand coordinated to the UO2 2+ ion. The complex [UO2(THMA)2]2+ (THMA=N,N,N′,N′-tetrahexylmalonamide) was prepared as the BF4− salt; this material tended to form an oil. However, [UO2(TMMA)2](OTf)2 (OTf=triflate) was isolated as a crystalline solid. Comparison of the Fourier transform infrared spectra of these complexes to the spectra of complexes formed in liquid–liquid extraction systems supports the hypothesis that complexes of the type [UO2(NO3)2L] and [UO2L2](NO3)2 (L=diamide extractant) form in the extraction systems.