Dioxouranium(VI) complexes with potential ter- and tetra-dentate Schiff base ligands

Abstract

A series of dioxouranium(VI) complexes were synthesised with the tetradentate Schiff base ligands (N 2O 2 donor set) obtained by the condensation of ethylenediamine with salicyladehyde(H 2salen), acetylacetone (H 2aaen) or benzoyl acetone (H 2baen) and ter-dentate Schiff base ligands derived by condensation of Salicylaldehyde with glycine(glysal), o-aminophenol(APhSal) or 2-amino 4-methyl pyridine (AMPy Sal) as well as glycine with acetylacetone (glyaa). The terdentate ligands have the NO 2 or N 2O donor set. The tetradentate ligands formed complexes of the type [UO 2LX 2], where L  H 2salen, H 2aaen, H 2baen and X  Cl, I, NO 3, NCS, 0.5 SO 4; and the complexes contain 6-coordinated UO 2 2+ group with the anions inside the coordination sphere. he IR evidence shows that the thiocyanate group is actually N-bonded iso-thiocyanato, the nitrato group is involved in unidentate covalent bonding and the sulphato group is bonded covalently in a bidentate manner. The far IR spectra was studied to find the ν(UCl) at 234 cm −1 and the δ (OUO) at ca. 225 cm −1. UO 2(ClO 4) 2 reacted with H 2salen to form UO 2(salen). The terdentate ligands H 2glysal and H 2glyaa formed complexes of the type UO 2(glysal)H 2O and UO 2(glyaa)2H 2O, which is confirmed on the basis of IR and DTG, TGA data. The UO 2 2+ group is 4- and 5-coordinated respectively, in these complexes. The potential ter-dentate ligands H 2APhSal and HAMPySal behaved essentially as bidentate ligands and formed 4-coordinate, neutral complexes, UO 2L 2 (L = H-APhSal or AMPySal). An examination of the mass spectra revealed neither the complex ions nor the metallated fragmentation products. The molecular ion and the ions of the fragmented molecules of the ligand were only observed. The thermal analysis indicates that in all cases U 3O 8 is obtained as the final thermal product. However, the uranyl sulphate complexes decompose via a thermally stable UO 2SO 4 phase to form U 3O 8 at higher temperatures. The equatorial coordination number of the UO 2 2+ ion in the complexes is thus either 4-, 5- or 6, giving a series of 6-, 7- or 8-coordinate uranium(VI) complexes.