Solid complexes of plutonylion with benzoyl (PMBP), acetyl (PMAP) and trifluoroacetyl (PMTFP) derivatives of 1-phenyl-3-methylpyrazol-5-one and various oxo donors such as dihexyl sulfoxide (DHSO), dioctyl sulfoxide (DOSO), dibutyl hexanamide (DBHA), dibutyl octanamide (DBOA) and dibutyl decanamide (DBDA) have been synthesized and characterized. Analytical data establish that sulfoxides form 11 adducts and have the stoichiometry PuO2·X2·Y (X=PMBP, PMAP and PMTFP) and Y=DHSO and DOSO while amides form 12 adducts of the type PuO2X2·2A where A=DBHA, DBOA and DBDA. The I. R. spectra of sulfoxide and amide complexes indicate that the ligands are O-bonded. Spectrophotometric investigations of the benzene solution of these complexes indicate a bathochromic shift of the 831 nm peak to 848–853 nm region, which confirms the retention of PuO
moiety in these synergistic adducts.