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-acetami dophenol (BIAAP) are studied on the basis of their analytical, spectroscopi c, 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(I ll) > Ni(II). The high stability of BIAAP towards Zn(II) and Cd(ll) over th e other ions is remarkable, in particular over Cu(ll), a fact that may be o f technological interest. The isolated complexes are found to have the gene ral 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. T he 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. Consid ering the higher stability of the Zn(ll) versus Cu(ll) complex, it is propo sed that this moiety may be of interest to design Zn selective complexing a nd/or extracting agents. (C) 2001 Elsevier Science Ltd. All rights reserved .