[en] The complexation of Th(IV) with desmethyldesferrithiocin (H₂DMDFT), a derivative of the siderophore desferrithiocin (H₂DFT), was studied by potentiometry, spectrophotometry and NMR. Three protonation constants of the ligand were determined by potentiometric titrations and ¹H-NMR and assigned to the phenolate group, the nitrogen at the hydroxypyridine ring, and the carboxylate group. The formation constant of the 1:2 complex, Th(DMDFT)₂, was determined by absorption spectrophotometry with oxalate as a competing ligand. A tridentate complex with Th(IV) involving the phenolate oxygen, the thiazoline nitrogen and the carboxylate group of H₂DMDFT was proposed. (orig.)