Thermodynamic study of complexation phenomena of some alkaline earth metal (II) complexes in propanol-1-water mixtures at various temperatures

The stability constants of Mg2+, Ca2+, Sr2+ and Ba2+ perchlorates with 2,4-diamino-3,5-dicyanothiophene (DADCT) have been determined at 15, 25, 35, 45 and 55 degreesC in 10, 20 and 30% (w/w) propanol-1-water mixtures using the conductometric technique. The conductometric data were analysed using a model 1: 1 stoichiometry by which the stability constants, K,, and the limiting molar conductance were obtained. The plots of specific conductance versus the molar ratio [A](o)/[Cn+](o) suggest that the stoichiometry of metal ion complexes is of a 1:1 complex. The stability constants tend to decrease with the atomic number as well as the ionic radii in the order Mg > Ca > Sr > Ba in 10% > 20% > 30% (w/w) propanol-1-water solvents. This trend was found to agree exactly with the Irving-Williams series for all the systems under investigation. The thermodynamic parameters, DeltaGdegrees, DeltaHdegrees and DeltaSdegrees, for the complexation processes of all the complexes were evaluated and their significances were discussed.