Yes, in general, complex formation is strongly exothermic.
Based on studies examining complex stability, the overall enthalpy terms associated with complex formation reactions tend to release heat, indicating an exothermic process. While the stability of the complex might not depend on specific factors such as the length of a substitution chain, the energy dynamics of the reaction itself usually favor heat release. The entropy values, however, tend to oppose complex formation, suggesting that enthalpy is the driving force in many complex formation reactions.
Essentially, the formation of a complex often involves the creation of new bonds or interactions, which release energy. This released energy manifests as heat, thereby making the process exothermic.
