Efficient separation of perrhenate as analogue to pertechnetate in nitric acid solution with a DOTA-tetraamide ligand: Solvent extraction, complexation and structure study

The two DOTA-tetraamide ligands, DOTAM- n -butyl (1,4,7,10-tetrakis[( N - n -butyl; carbamoyl)methyl]-1,4,7,10-tetraazacyclododecane) and DOTAM-benzyl (1,4,7,10- tetrakis[( N -benzylcarbamoyl)methyl]-1,4,7,10-tetraazacyclododecane), were synthesized and characterized by MS, NMR and FTIR spectra. In acid solution, DOTAM- n -butyl was liable to be protonated. FTIR, 1 H NMR, ESI-MS spectra and X-ray diffraction analyses revealed that the nitrogen atoms of cyclen ring combined two protons to form a cation with two positive charges. The protonated DOTAM- n -butyl had strong extraction ability and good selectivity for ReO 4 − . It was extracted by means of the substitution of one ReO 4 − for one NO 3 − in the 1:2 complex of DOTAM- n -butyl with HNO 3 . The solvent extraction and X-ray crystallography demonstrated an anion-exchange extraction model. Meanwhile, X-ray crystal structure analyses of ligand complexes with HReO 4 or HNO 3 also indicated that ReO 4 − or NO 3 − ions were located in the gap between the upper and lower protonated ligands through multiple hydrogen bonds and electrostatic interactions.