Skip to the content.

[Non-critical IUPAC compilation] [Critical IUPAC publication of solubility data]

Critical IUPAC publication of equilibrium data


In 1977 the Commission on Equilibrium Data of the Analytical Division of IUPAC (now IUPAC Subcommittee on Solubility and Equilibrium Data (SSED)) started to promote the writing of critical surveys of stability constants of metal complexes of specific ligands or small groups of related ligands. Each survey was prepared by experts working actively in the field of thermodynamics of complexes, and commented on by the members of the Commission on Equilibria Data.

As part of the critical assessment, data were classified in four categories: recommended, tentative, doubtful and rejected. According to the first IUPAC regulations, the data could be recommended (R) if the results of at least two independent research groups are in good agreement; if the surveyor has no doubt as to the adequacy of the applied experimental and calculation procedure; if the consideration of the activity concentration relation is correct, and the standard state is unambiguous. The given error of such a constant must be no less than ±0.05 logarithmic units. Data could be regarded as tentative (T) if all the conditions mentioned for R category are fulfilled, except the first one; or if the surveyor observes some deviation from the necessary rigorousness, but this probably caused no serious mistakes. The given error of such a constant must not exceed ±0.2 logarithmic units. Data should be considered as doubtful (D) if the surveyor suspects some errors in the evaluation of the constants, which are nevertheless of semi quantitative value. The probable error of such a constant should not exceed ±0.2 logarithmic units. Data determined by either an inadequate method, or under undefined conditions should be rejected (Rj). The same category is given if any serious objection is found in the evaluation.

More recently, criteria have been modified and literature data have been accepted as reliable (designated “reported” in relevant Tables), and thus included in the regression analyses, when all, or in some cases most, of the following requirements have been met: (i) full experimental details are reported (solution stoichiometry, electrode calibration method, temperature, ionic strength, error analysis); (ii) the equilibrium model is considered to be complete (including hydrolysis reactions); (iii) data were measured in an essentially non-complexing medium; and (iv) the experimental method and numerical analysis are considered to have minimal systematic errors.


List of published surveys :

Ligand or system1 Reference
EDTA Anderegg (1977)
1,10-Phenantroline, 2,2’-bipyridyl and related compounds McBryde (1978)
8-hydroxyquinoline Starý et al. (1979)
Fluoride Bond and Hefter (1980)
Acetylacetone Starý and Lijenzin (1982)
NTA Anderegg (1982)
Indium Tuck (1983)
Histidine, phenylalanine, tyrosine, L-DOPA and tryptophan Pettit (1984)
Ethylenediamine Paoletti (1984)
Cyano complexes Beck (1987)
Nucleotide complexes Smith et al. (1991)
Glycines Kiss et al. (1991)
Alanine, Valine, Leucine Sovágó et al. (1993)
Cysteine, Cystine, Methionine, Serine, Threonine, Asparagine, Glutamine Berthon (1995)
Arginine, Lysine, Ornithine Yamauchi and Odani (1996)
Salicylic acid and other aromatic hydroxycarboxylic acids Lajunen et al. (1997)
Phosphonic acids Ρopov et al. (2001)
Crown ethers Arnaud-Neu et al. (2003)
Aliphatic hydroxo-acids Portanova et al. (2003)
IDA, MIDA, DTPA, TTHA, DOTA, NOTA, TETA Anderegg et al. (2005)
Hg2+ + OH-, Cl-, CO32-, SO42-, and PO43- Powell et al. (2005)
Cu2+ + OH-, Cl-, CO32-, SO42-, and PO43- Powell et al. (2007)
Pb2+ + OH-, Cl-, CO32-, SO42-, and PO43- Powell et al. (2009)
Cd2+ + OH-, Cl-, CO32-, SO42-, and PO43- Powell et al. (2011)
Zn2+ + OH-, Cl-, CO32-, SO42-, and PO43- Powell et al. (2013)

The recent reviews have been prepared by the same group of experts scrutinising data reported in the SC-Database. Detailed discussions of the pros and cons of each decision in the selection of the recommended constants from the literature values are given in each report.


The critical reviews published in Pure & Applied Chemistry until 2013 can be downloaded for free. In 2014 the publishing rights for new reviews were obtained by De Gruyter (although no new reviews have appeared since that time) and therefore may attract a fee for access.

  1. Abbreviations: MIDA - Methyliminodiacetic acid; TTHA - Triethylenetetraminehexaacetic acid; NOTA - 1,4,7-Triazacyclononane-N,N’,N’‘-triacetic acid; TETA -Triethylenetetramine; DOTA - 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid.