Enthalpy/Entropy Compensation in the Melting of Thermotropic Nitrogen-Containing Chelating Ligands and Their Lanthanide Complexes: Successes and Failures

In this short overview dedicated to the thermodynamics of liquid crystalline chelating nitrogen-containing ligands and their lanthanide complexes (i.e., lanthanidomesogens), we first go through the initial successes obtained with the introduction of the concept of enthalpy/entropy compensation for rationalizing and programming melting and clearing temperatures in thermotropic mesophases. In the second part, the failures encountered during our attempts for switching from a qualitative toward a quantitative interpretation of the melting processes in polycatenar lanthanidomesogens are discussed, together with the delicate correlations established between the thermodynamic parameters of intermolecular cohesion measured in noncoordinating solvents and those operating in pure mesophases.