Abstract
The diiminedithiophene amine ligands, 2,10-dithiophene-3,6,9-triaza- 2,10-undecadiene (2,2-DIDTA), 2,11-dithiophene-3,6,10-triaza-2,11-do- decadiene (2,3-DIDTA) and 2,12-dithiophene-3,7,11-triaza-2,12-tri- decadiene (3,3-DIDTA) were synthesized. These compounds have been characterized correctly by the study of some physical methods, such as infrared spectroscopy, nuclear magnetic resonance spectroscopy, mass spectroscopy, elemental analysis and so on. The protonation constants of 2,2-DIDTA, 2,3-DIDTA and 3,3-DIDTA were determined potentiometrically in 10% CH3OH + 90% H2O containing 0.10M (CH3)4NCl and the temperature was maintained at 25.0 ± 0.1ºC. The obtained different values of protonation constants are due to the different number of carbon atoms present in diiminedithiophene amine ligands. At the same time, the stability constants of copper(II) and nickel(II) complexes of these ligands could be determined. It was found that the sequence of stability constants could be influenced by three factors: First, The sizes of chelate rings; Second, the ring strain of the chelate rings; Third, the basicity of the ligands. The acid dissociation kinetics of diiminedithiophene amine copper(II) complexes have been studied in 0.50M (NaClO4+HClO4) aqueous solution at 25.0 ± 0.1ºC using stopped-flow techniques, and the general acid catalysis phenomenon would be found. The cleavage of Cu－N bond might have some probable pathways. In the current investigation, the factors affecting the relative importance of each of these possible pathways were discussed. The rate-determining step of linear complexes or macrocyclic complexes is discussed. The proton transfer is the rate-determining step in our work. Finally, the complexes, Cu(2,2-DIDTA)2+, Cu(2,3-DIDTA)2+ and Cu(3,3-DIDTA)2+ were subjected to react with monodentate ligands. Using spectrophotometric method and Rose Drago equation, we obtained their equilibrium constants. The obtained different values of equilibrium constants of complexes are explained by their structures and softness and basicity of monodentate ligands. These constants could be quantitatively correlated by Edwards equation. The values of a, b and a/b for the copper(II) complexes were reported and the factors which influence these values were discussed. Then, we could know that these three copper(II) complexes were soft acid.