Ultraviolet Spectroscopic Determination of the Stabilities of Weak Organic Complexes

The methods described in the literature for the determination of the stability constants K and extinction coefficients ε of weak organic electron-donating and electron-accepting complexes are discussed. It is shown that the majority of the methods based on a combination of the Bouguer–Beer–Lambert law and the law of mass action and involving the use of an excess of one component suffer from the same disadvantages as the parent spectrophotometric method – the Benesi–Hildebrand method (the inconsistency between K and ε, the appearance of negative values of K, the dependence of K on the wavelength used, the dependence of K and ε on the relative amounts of the donor and acceptor, etc.). The reliability criteria of Pearson and Deranleau are discussed and their limitations are demonstrated. It is suggested that the absolute values of K and ε obtained spectrophotometrically are of interest only from a comparison of complex formation in series of organic compounds with similar structures and that all measurements should as far as possible be made under identical conditions. The review covers studies published up to the middle of 1973.
The bibliography includes 177 references.