The chemistry of the trivalent actinoids. Part 5. Uranium(III) complexes with bidentate organic amides

Abstract

Uranium(III) forms air-sensitive tetrakis complexes with the amides Me₂N·CO·[CH₂]_n·CO·NMe₂ and Me₂N·CO·CH₂·CMe₂·CH₂·CO·NMe₂[series (I; n= 1–4)] and Et₂N·CO·[CH₂]_n·CO·NEt₂ and Et₂N·CO·CH₂·CMe₂·CH₂·CO·NEt₂[series (II; n= 1–4)] using [BPh₄]^– or [PF₆]^– as the counter anion. The i.r. spectral results indicate interaction through the ligand oxygen atoms and non-participation of the anions in co-ordination, leading to the UO₈ chromophore which has low symmetry. The complexes are black, mauve, or green. Differences in the energies of f–d transitions are explained in terms of nephelauxetic effects. Similar changes have been observed in the energies of bands observed at shorter wavelengths, which are assigned to metal ion-to-ligand electron transfer. The spectra of NNN′N′-tetramethyldiamide and corresponding NNN′N′-tetraethyldiamide complexes are not noticeably different, indicating that changes in the N-alkyl substitution pattern may have little effect on amide base strength. The magnetic properties of the NNN′N′-tetramethylmalonamide complex with tetraphenylborate are normal for U^III with µ_eff.(294 K)= 2.97 B.M. With 4,4′-methylenebis[1,5-dimethyl-2-phenylpyrazol-3(2H)-one], air-sensitive, lilac-mauve, tris complexes have been prepared with the same anions. The change in stoicheiometry is attributed to steric effects but, apart from a broadening of the f–d transitions, there are no obvious spectral effects which distinguish the UO₆ chromophore.