Pentacoordinated Cu(II)/Zn(II) complexes bearing macrocyclic skeleton: synthesis, spectroscopic and molecular structure optimization studies

2,6-Diacetylpyridine and 1,2-diaminoethane in the presence of copper(II) and zinc(II) chlorides containing a few drops of acetic acid were condensed into compositions [CuLH2]2·2HCl·H2O (1), [Cu2LPyz]2·2HCl·4CH3COCH3 (2) [CuZnLPyz]2·2HCl·2CH3COCH3·10H2O (3) and [ZnL'Cl]3·3HCl·3H2O (4) substantiated by elemental analyses, IR, UV-vis, 1H NMR and FAB mass spectral data. Demetallation of a Ni(II) complex (isolated as above) afforded macrocyclic skeleton LH4, whereas L' symbolizes a skeleton of the ligand containing only ethylenediamine and 2,6-diacetylpyridine. Molecular structure optimization using MM2 force field calculations for the complexes revealed distorted square pyramidal geometry around Cu(II) centers in complexes 1 and 2 and tetrahedral geometry around Cu(II) and Zn(II) centers with different degrees of distortion in complex 3 whereas three Zn(II) atoms (each in distorted square pyramidal geometry) attached via Cl bridges form a cyclic structure in complex 4. In complexes 1 and 2,Cu-Cu = 2.63-2.66 Å indicated the possibility of coupling between the two Cu(II) centers which has been supported by lower magnetic moment as well as ESR spectra showing half-field signal.