Electric conductance and semi-empirical studies on two thiophene derivatives/metal cation complexation

The formation constants for 1:1 Stoichiometric complexes of 2,4-diamino-3,5-dicyano thiophene (DADCT) and 2-amino cyclohexane thiophene-3-carbonitrile (ACTC) with transition metal cations (Mn⁺² , Ni^+ 2 , Cu^+ 2 , Zn^+ 2 , Cd^+ 2 , UO₂^+ 2 , La^+ 3 and Zr^+ 4 ) in 50% (V./V.) ethanol–water and methanol–water solvents have been determined conductometrically at different temperatures. A semi-empirical PM3 calculations were also used to predict the structure of the metal complex by calculating the enthalpy of formation, the geometrical parameters and Mulliken charges of the free ligands and the suggested structures of the formed complexes. The values of the different thermodynamic parameters (ΔG, ΔH and ΔS) have been obtained. The results show that the complexation reactions are all exothermic except in the case of La^+ 3-DADCT, which is endothermic reaction. The formation constant for the transition metal cations-ACTC complexes were larger than that for the transition metal cations-DADCT complexes. Also, the formation constants for all studied complexes in ethanol–water solvent were higher than that in methanol–water solvent. Using the SPSS computer program, a second order relation was found between Log k and the ionic radius (r) of the cations under investigation. The semi-empirical PM3 calculations show that there are two suggested structures of the complexation of (DADCT) with the studied metal ions.