Previously, the halide complex formation of the group-5 elements had been studied in mixed HCl/HF solutions by their extraction into triisooctyl amine (TiOA). The extraction sequence Ta > Nb > 105 > Pa was observed, while theoretical calculations performed for the pure chloride system predict the reversed sequence of extraction. To verify this experimentally, new batch extraction experiments for Nb, Ta, and Pa from pure HCl-, HBr-, and HF solutions were performed with various aliphatic amines. Based on these results, new reversed-phase micro chromatographic column separations were elaborated using the quaternary ammonium salt Aliquat 336 on an inert support in the computer-controlled chromatography apparatus ARCA II. In the system Aliquat 336(F-)/HF, after feeding of the activity onto the column in 0.5 M HF, element 105 did not elute in 4 M HF (Pa fraction) but showed a higher distribution coefficient (>570), close to that of Nb land Ta). In the system Aliquat 336(Cl-)/ HCl, after feeding onto the column in 10 M HCl, element 105 showed a distribution coefficient in 6 M HCl (similar to 438) close to that of Nb establishing the extraction sequence Pa > Nb greater than or equal to 105 > Ta. Exactly this sequence has been predicted theoretically based on relativistic calculations of the electronic structure of hydrolzed species of Nb, Ta, Pa, and element 105, and of their various complexes formed in HCl solutions, i.e. by explicitly considering the competition between hydrolysis and complex formation. In this way, the extraction sequence fluorides much greater than chlorides > bromides for the group-5 halide complexes is also correctly predicted.
