Selective solvent extraction of tetrahedrally-coordinating transition metal ions from acidic aqueous media using benzimidazole-phosphinate ligands: specificity for zinc(II) over copper(II)

The synthesis, solution complexation behaviour and solvent extraction abili ty of related chelating mono-and bis-(benzimidazole)phosphinate ligands 8 a nd 9 has been assessed. P-31 NMR, fluorescence and absorption spectroscopy and electrospray mass spectrometry revealed preferential formation of 1 : 1 complexes with the divalent ions Zn, Co and Ni, and ML2 complex formation with the bidentate ligand. Extraction studies showed that 9 extracted Zn > Co much greater than Ni with no extraction of copper(II), but avid extracti on of copper(I), generated in situ, consistent with the ligand's preference for the binding of tetrahedrally-coordinating metal ions.