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[Critical IUPAC publication of equilibrium data]

Non-critical IUPAC compilation


For many years, the International Union of Pure and Applied Chemistry (IUPAC) sponsored a non-critical compilation of metal complex equilibrium constants. The result was the publication of two small and four large volumes of stability constants. The initial volumes were edited by J. Bjerrum, G. Schwarzenbach and L.G. Sillén (19571, 19582). The first major volume, edited by L.G. Sillén (for inorganic ligands) and A.E. Martell (for organic ligands), was published in 1964 (Sillén et al. 19643). The second volume, subtitled supplement No. 1, edited by L.G. Sillén and E. Högfeldt (for inorganic ligands) and A.E. Martell and R.M. Smith (for organic ligands), was published in 1971 and covered the literature through 1968 (Sillén et al. 19714). Further work by Perrin (19795) and Högfeldt (19826) produced two additional volumes of stability constants covering equilibria with organic and inorganic ligands that appeared in the literature up to 1974. The larger compilations attempted to include all papers in the field related to metal complex equilibria. In 1990, a computerised database containing the values from the IUPAC volumes was created by L. Pettit. The database – known as SC-Database – was distributed by Pettit’s company Academic Software and was kept up to date with new values from the literature with the help of an extended team.


The IUPAC volumes and SC-Database aimed to include all published constants with no assessment of their quality. Most of the papers published in the twentieth century that contained stability constants, enthalpies, entropies and free energies of metal complexes in both aqueous and non-aqueous media were compiled. In one of the later versions of the SC-Database, it was noted that fewer than 32 % of the data had originated with the IUPAC volumes (i.e. before 1974) and that as of 2005, some 107’900 records for 9’200 ligands coming from 22’500 references were contained in the SC-Database. However Pettit and Pettit (2009) would later write that “New stability constants reported in the literature are now, in general, not designed for general use by other scientists. Rather, they are measured to confirm a reaction mechanism or to identify bonding centers. The ligands studied are becoming more esoteric (e.g., calixarenes, or long-chain peptides), and the constants are often measured less rigorously and to a lower precision than earlier measurements. As a result, the constants are frequently of less general use and are less appropriate for inclusion in the IUPAC Stability Constants Database. The abstraction and compilation of new literature data will, therefore, probably cease during 2009 but the database will continue as an invaluable and irreplaceable resource, which should be maintained and made available into the future.” However, this has not been the case (see below).


The IUPAC volumes are still be available in some science libraries and can also be obtained at relatively low cost from online / second-hand bookstores. The SC-Database was still being distributed by Academic Software until 2016-17 but is no longer available. Files resulting from metal queries can be found here.

  1. Bjerrum, J., Schwarzenbach, G., Sillén, L.G., 1957. Stability Constants for Metal-Ion Complexes. Part I. Special Publication no. 6. Chemical Society, London., UK. 

  2. Bjerrum, J., Schwarzenbach, G., Sillén, L.G., 1958. Stability Constants for Metal-Ion Complexes. Part II. Special Publication no. 7. Chemical Society, London, UK. 

  3. Sillén, L.G., Martell, 1964. Stability Constants of Metal Complexes. Special Publication no. 17. Chemical Society, London, UK. 

  4. Sillén, L.G., Högfeldt, E., Martell, A.E., Smith, R.M., 1971. Stability Constants Supplement no. 1, Special Publication no. 25. Chemical Society, London, UK. 

  5. Perrin, L.D., 1979. Stability Constants of Metal-Ion Complexes: Part B. Organic Ligands. IUPAC Chemical Data Series no. 22. Pergamon Press, Oxford, UK. 

  6. Högfeldt, E., 1982. Stability Constants of Metal-Ion Complexes: Part A. Inorganic Ligands. IUPAC Chemical Data Series no. 21. Pergamon Press, Oxford, UK.