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 ability of related chelating mono- and bis-(benzimidazole)phosphinate ligands 8 and 9 has been assessed. ³¹P 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 >> Ni with no extraction of copper(n), but avid extraction of copper(I), generated in situ, consistent with the ligand's preference for the binding of tetrahedrally-coordinating metal ions.