Abstract Established ligand design principles are extended to transuranium elements and were tested out for Pu(IV) complexation by the trihydroxamic acids, desferrioxamine B (DFB) and N,N′,N″-tris[2-( N- hydroxycarbamoyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH). Nd(III) was used as a simulant for Am(III) to characterise its complexation with BAMTPH. Log K 1 values for Pu were measured using an optical fibre system coupled to a spectrophotometer and were found to be 30.8±0.1 and 30.0±0.2 for the Pu(IV)-DFB and Pu(IV)-BAMTPH complexes, respectively. The stability constant for the Nd-BAMTPH complex was measured potentiometrically and was found to be 16.7±0.01. These values were plotted onto existing correlations between log K 1(L) versus log K 1(OH −1) and found to fit very well.