Abstract
The formation equilibria of the dimethyltin(IV) complexes with of N,N,N',N'-tetraethylethylenediamine (Et(4)en) in solution were investigated. The stoichiometry and stability constants of the complexes formed in solution phase were determined at different temperatures (15 degrees C - 35 degrees C) and in solutions of dioxane-water mixtures of different compositions (15% - 62.5%). The accepted model is composed of the 110, 111, 11-1 and 11-2 species. The thermodynamic parameters Delta H degrees and Delta S degrees associated with the protonation of N,N,N'-tetraethylethylendiamine (Et(4)en) and its complex formation with the dimethyltin(IV) species were determined. The complex formation reaction is exothermic. The equilibrium constant for the displacement of N,N,N',N'-tetraethylethylenediamine coordinated to dimethyltin(IV) by some selected DNA constituents was calculated. The K-eq values clearly indicate the ability of DNA to displace the coordinated Et(4)en from its dimethyltin(IV) complex. The nucleotides IMP and GMP have the highest values. The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program. Also the vibrational frequencies of the ligands and complexes were computed for the optimized geometries. The results shows that there is no imaginary frequencies as found in the calculated vibrational frequencies. The binding energies of the dimethyltin(IV) complexes were calculated. All calculated binding energy values are negative.