We present a relativistic density functional study on some plutonium compounds with thenoyltrifluoroacetone and similar ligands which can be used in the extraction of plutonium. The method of effective core potentials is used on plutonium. The binding energies of the complexes of plutonium in the formal oxidation states II, IV and VI have been determined and the geometries of some of the complexes have been fully optimized. The stability of the compounds in the different oxidation states and the effect of varying the side groups in the ligands are discussed. Comparisons with analogous uranium compounds are presented.