Estimation of Thermodynamic Properties of Aqueous Iron and Cobalt Ammines at Elevated Temperatures

Models based on the Lewis formulation of the Criss–Cobble correspondence principle to predict the thermodynamic stability constants for iron and cobalt ammines at high temperatures are proposed. The thermodynamic study of metal complexes is of interest because there is a lack of this data at high temperatures in the literature. In this article, the results of the Criss–Cobble model for simple cations were used to compare the predicted stability of iron and cobalt ammines at high temperatures with the available experimental data. The Lewis formulation of the Criss–Cobble model was fitted to the available experimental data in order to provide a simpler basis for the prediction of the thermodynamic behavior of iron and cobalt ammine complexes at elevated temperatures. Based on the available experimental data, it was found that the simple cation model was perfectly adequate to predict the thermodynamic stability of cobalt ammines at high temperatures. For iron ammines, there were some variations at elevated temperatures between the simple cation model and the new model.