Synthesis and characterization of Ni(II), Cu(II) and Zn(II) complexes with new macrocyclic Schiff base ligands containing piperazine moiety

Two new macrocyclic Schiff base ligands L1 and L2 from [1 + 1] and [2 + 2] condensation reaction, respectively, have been obtained in a one-pot synthesis starting from 1,4-bis(2-formylphenyl)piperazine and 2,2-dimethyl-propylendiamine. Unfortunately, because of the low solubility of two products, we were unable to separate them effectively. Macrocyclic Schiff base complexes [NiL1](ClO4)2, [CuL1](ClO4)2 and [ZnL1](ClO4)2 were prepared from the reaction of a mixture of L1 and L2 in the presence of nickel(II), copper(II) and zinc(II) metal ions, respectively. In all cases, only [1 + 1] condensation products were obtained and no metal complexes were isolated with the L2 macrocycle. All of complexes have been characterized by elemental analysis, IR spectra, FAB-MS, conductivity measurements and in the case of Zn(II) complex by 1H and 13C NMR spectroscopy. Crystal structures of [NiL1](ClO4)2 and [NiL1′](ClO4)2 complexes have been also determined. The Ni(II) is coordinated to the ligand L1 and L1′ by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry.