Free-energy relationships in coordination chemistry. II. Requirements for linear relationships

This paper discusses factors predisposing to linear free energy relationships among families of metal complexes. It is postulated that changes occurring at a reaction site in a test series of reactions and the corresponding changes in a reference series have their origins in the same independent variables. Linearity is seen to be favored when changes in the reaction site or in ligand substituents are small, and in the absence of strong interactions with the solvent. In addition to such considerations of a molecular sort, a number of relationships among the thermodynamic quantities ΔH 0 , ΔS 0 , and ΔG 0 which have been identified as having a significant influence on rate and equilibrium relationships in series of organic reactions are discussed in terms of their effect on metal–ligand systems.