The ECW model

This paper updates some of the traditional uses of the ECW model involving enthalpies but emphasizes the often overlooked applications of the parameters as a scale to analyze reactivity and spectroscopy. The importance of having this fundamental understanding of the ECW model is emphasized by current research literature where new uses and extension of the ECW model are presented. Interactions between ions and neutral species have been explored (19), and new insights about the "anomalous" basicity order of the amines obtained (20). The role solvent plays in determining the donor order of anions also is discussed quantitatively in the context of this model. Bond dissociation energies are correlated by the addition of a transfer term, T, to the model (21). The ECT data fit has an impact on the current view of electronegativities (22). The addition of organometallic bond energies (23) to the ECT model has many implications for understanding the reactivity of organometallic compounds. The derivation of substituent constant parameters, ΔEx and ΔCx, for X-substituents correlates data that previously required σ, σI, σR, σ+, etc. scales (24). In general, the properties of coordination and organometallic compounds have different C/E ratios than the organic reactions that form the basis of the σ- scales. The spectroscopies and reactivities of these systems are poorly correlated by the σ- scales. Recent work illustrates the utility of the electrostatic-covalent models for interpreting this chemistry (25, 26). Finally, solvation effects are correlated by treating the specific interaction with ECW (27) and the nonspecific interactions with solvent polarity parameters (28). With the impact of the ECW and ECT models on so many fields of chemistry and on the analysis of research results in the areas of chemical reactivity and spectroscopy, the basic methodology and philosophy of this approach is appearing in all modern textbooks of inorganic chemistry (1).