Ion-pair extraction behavior of divalent transition metal cations as charged complexes with N,N-bis(2-pyridylmethylidene)-1,2-diiminoethane and its analogues

The use of neutral di-Schiff base ligands, N,Nʹ-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) and its analogues, N,Nʹ-bis[1-(2-pyridyl)ethylidene]-1,2-diiminoethane (BPEE) and N,Nʹ-bis(2-pyridylmethylidene)-trans-1,2-diiminocyclohexane (BPIC), as complexation reagents for ion-pair extraction of divalent transition metal cations into nitrobenzene with picrate anion was investigated. The results of numerical analysis concerning the extraction behavior indicated that they act as imine-N bidentate ligands in the extraction system. Furthermore, the introduction of the alkyl substituents onto imine-C on BPIE led to the change in the extraction selectivity by steric distortion of the cationic complexes, whereas that onto ethylene-C only caused the enhancement of the extractability.