AbstractThe 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 °C 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, Ks, and the limiting molar conductance were obtained. The plots of specific conductance versus the molar ratio [A]o/[Cn+]osuggest 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, ΔGo, ΔHoand ΔSo, for the complexation processes of all the complexes were evaluated and their significa