Coordination of uranyl bis(thenoyl trifluoroacetonate) with some heterocyclic n-oxides

Abstract

Organic phase equilibrium constants of the synergistic systems, UO 2 2+/thenoyl trifluoroacetone (TTA)/heterocyclic N-oxide/chloroform were determined by the solvent extraction procedure. Free base concentrations were determined in a single step spectrophotometrically. The results indicate that the equilibrium constants of the systems with the various N-oxides follow the trend 2:6 dimethyl pyridine N-oxide (2:6 DMPO) < pyridine N-oxide (PyO) < 2 methyl pyridine N-oxide (2 MPO) < 3 methyl pyridine N-oxide (3 MPO) < 4 methyl pyridine N-oxide (4 MPO). The deviation of 2:6 dimethyl and 2 methyl pyridine N-oxides from the p K a order of the series has been attributed to the occurrence of steric effects with these ligands. No evidence is observed for back donation of electrons from the uranyl group to the π ∗ antibonding orbital of the N-oxide ligand.