Ion-pair extraction behavior of transition metal(II) cations as charged complexes with ethylenediamine derivatives having heterocyclic pendant arms

The use of N,N,N′,N′-tetrakis(1′-pyrazolylmethyl)-1,2-diaminoethane (tpzen), N,N,N′,N′-tetrakis(3′,5′-dimethylpyrazol-1′-ylmethyl)-1, 2-diaminoethane (Me8tpzen) and N,N,N′,N′-tetrakis(2′-pyridylmethyl)-1,2-diaminoethane (tpen) as complexation reagents for ion-pair extraction of metal(II) cations into nitrobenzene was investigated. The order of extractability of the metals was tpen > Me8tpzen > tpen. Although these molecules have four nitrogen-containing heterocyclic pendant arms and act as sexadentate ligands normally in aqueous solution, the result of numerical analysis concerning the extraction behavior indicated that they act as bidentate ligands in the extraction system. The pendant arms were not concerned in chelate formation and the arms acted to raise the hydrophobicity and the extractability of the complexes.