Over the past fifteen years the Commission on Equilibrium Data of the
Analytical Division of the Inter- national Union of Pure and Applied
Chemistry has been sponsoring a noncritical compilation of metal complex
formation constants and related equilibrium constants. This work was
extensive in scope and resulted in the publication of two large volumes
of Stability Constants by the Chemical Society (London). The first
volume, edited by L. G. Sillen (for inorganic ligands) and by A. E.
Martell (for organic ligands), was published in 1964 and covered the
literature through 1962. The second volume, subtitled Supplement No. 1,
edited by L. G. Sillen and E. Hogfeldt (for inorganic ligands) and by A.
E. Martell and R. M. Smith (for organic ligands), was published in 1971
and covered the literature up to 1969. These two large compilations
attempted to cover all papers in the field related to metal complex
equilibria (heats, entropies, and free energies). Since it was the
policy of the Commission during that period to avoid decisions
concerning the quality and reliability of the published work, the
compilation would frequently contain from ten to twenty values for a
single equilibrium constant. In many cases the values would differ by
one or even two orders of magnitude, thus frustrating readers who wanted
to use the data without doing the extensive literature study necessary
to determine the correct value of the constant in question.