Highly selective extraction of Cu(II) and Zn(II) using [B(3-iPrpz) 4] − (iPrpz=isopropylpyrazolyl)

Abstract

The solvent extraction of first-series transition metal ions {Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)} with [B(3-iPrpz) 4] − (iPrpz=isopropylpyrazolyl) is reported. Although the previously reported tetrakis(pyrazolyl)borates, [B(pz) 4] − and [B(3-Mepz) 4] −, quantitatively extracted all the studied transition metal ions, [B(3-iPrpz) 4] − extracted only Cu(II) and Zn(II). In order to elucidate the origin of the selectivity, the structures of the extracted species, [B(3-iPrpz) 4] 2Zn ( 1) and [B(3-iPrpz) 4]Cu(OCOCH 3) ( 2), were determined by single-crystal X-ray diffraction. Complex 1 has a tetrahedral geometry with each ligand having bidentate coordination. Complex 2 has a distorted square pyramidal geometry with [B(3-iPrpz) 4] − having tridentate coordination and the acetate anion having asymmetric bidentate coordination. These structures of the extracted species are different from those of the previously studied tetrakis(pyrazolyl)borates, which are octahedral A 2M with each ligand having tridentate coordination (A −=tetrakis(pyrazolyl)borate, M 2+=first-series transition metal ion). Because the bulky isopropyl groups at the 3-position of the pyrazolyl ring prevent octahedral geometry, the other metal ions cannot form stable and extractable complexes with [B(3-iPrpz) 4] −.