New uranyl(VI) complexes: binding of mono and bidentate ligands to UO₂(tridentate) species

Abstract

New species of the type UO₂T·D, UO₂T·D·H₂O and UO₂T·DD are described (T = tridentate dianionic Schiff base ligand; D = monodentate donor e.g., H₂O, dmf, dmso, py etc.; DD = bidentate donor e.g., 2,2′-bipyridyl). The infrared, pmr and thermal analyses data of the complexes are reported. The ν₃ frequency of the dioxouranium(VI) moiety is seen in the region 880–925 cm⁻¹. While this frequency is not very sensitive to the nature of D, on the average ν₃ with D = nitrogen donor is smaller than that with D = oxygen donor. Sufficient solubility for NMR work exists only in strongly donor solvents (py or dmso). In such solutions D is displaced by the solvent. On heating, complexes generally lose H₂O, D or DD in one or more steps endothermically. The DD complexes are particularly stable and loss of DD occurs only at relatively high temperatures. It is proposed that the complexes are generally pentagonal bipyramidal. The five coordination positions on the equator are occupied by the combination of T and D, H₂O or DD. In the case of UO₂TD a dimeric T-bridged structure is likely. The dramatic stereochemical difference between UO₂T·D and MoO₂T·D is noted.