Complexes of 2-(2-benzimidazolylazo)-4-acetamidophenol, a phenoldiazenyl-containing ligand. Could this be a moiety suitable for Zn and Cd extraction?

The preparation and structural identification of new Fc(III), Co(II), Ni(ll), Cu(ll), Zn(ll) and Cd(ll) complexes of 2-(2-benzimidazolylazo)-4-acetamidophenol (BIAAP) are studied on the basis of their analytical, spectroscopic, magnetic and conductance data. The dissociation constant of the BIAAP as well as the stability constant of its metal complexes have been determined by spectrophotometric methods. The stability of the complexes follows the sequence: Zn(ll) > Cd(ll) much greater than Co(ll) > Cu(II) similar to Fe(Ill) > Ni(II). The high stability of BIAAP towards Zn(II) and Cd(ll) over the other ions is remarkable, in particular over Cu(ll), a fact that may be of technological interest. The isolated complexes are found to have the general formulae [M(BIAAP)(2)].xH(2)O (M = Co(ll), Ni(ll), Cu(ll) (x = 4), M = Zn(ll), Cd(ll) (x = 2)) or [Fe(BIAAP)(2)]Cl.2H(2)O. Structural information has been taken from spectroscopic, magnetic and conductance measurements. The coordination number of the metal ions is found to be six (Fe(III), Co(II), Ni(ll) and Cu(II)) and four (Zn(ll) and Cd(Il)) with binding through the phenolate O, azo N and, if necessary with the imidazole N3 atom. For Zn(II) and Cd(II) the phenoldiazenyl moiety seems to be the relevant one. Considering the higher stability of the Zn(ll) versus Cu(ll) complex, it is proposed that this moiety may be of interest to design Zn selective complexing and/or extracting agents. (C) 2001 Elsevier Science Ltd. All rights reserved.