Chemistry II Bonding

A successful bonding theory must be consistent with experimental data. This chapter reviews experimental observations that have been made on coordination complexes, and describes electronic structure and bonding theories used to account for the properties of these complexes. 

A critical objective of any bonding theory is to explain the energies of chemical compounds. Inorganic chemists frequently use stability constants, sometimes called formation constants, as indicators of bonding strength. These are equilibrium constants for reactions that form coordination complexes. Here are two examples of the formation of coordination complexes and their stability constant expressions  

Data from R. M. Smith and A. E. Martell, Critical Stability Constants, VoL 4, Inorganic Complexes, Plenum EVess, New York, 1976, pp. 40-42,96-119. Not all ionic strengths were identical for these detmninations, but the trends in K values shown here are consistent widi determinations at a variety of ionic strengths. 

Enthalpies of reaction can be measured by calorimetric techniques. Alternatively, the temperature dependence of equilibrium constants can be used to determine A/f° and A5° for these ligand substitution reactions by plotting In K versus /T. 

Thermodynamic parameters such as A//°, A5 , and the dependence of K with T are useful for comparing reactions of different metal ions reacting with the same ligand or a series of different ligands reacting with the same metal ion. When these data are available for a set of related reactions, correlations between these thermodynamic parameters and the electronic structure of the complexes can sometimes be postulated. However, exclusive knowledge of the A//° and A.S° for a formation reaction is rarely sufficient to predict important characteristics of coordination complexes such as their structures or formulas. 

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