Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.


NIST Critically Selected Stability Constants of Metal Complexes: Version 8.0

This database has been discontinued.

 Click here to download a copy of Critical Stability.

Version 8.0 is a major enhancement to this widely used database which provides comprehensive coverage of interactions for aqueous systems of organic and inorganic ligands with protons and various metal ions and is based on the six-volume Critical Stability Constants by Martell and Smith. The new version contains 225 additional ligands, new data, data printing, rapid bibliography searching and more streamlined commands. New literature has resulted in revision and upgrading of 30% of previous data. Entire contents are critically selected for accuracy and consistency.

For 6166 Ligands:

  • 112559 lines of data
  • metal stability constants and related equilibrium constants
  • thermodynamic constants
  • a complete bibliography
  • structural formulas
  • search by empirical formulas and type of ligand
  • protonation constants under specified conditions of temperature and ionic strength
  • heats of protonation
  • entropies of protonation
  • metal/metal species searching capabilities
  • author search

System Requirements: PC running WindowsTM 95, 98, 2000, NT 4.0 Me,XP and Vista 32 bit operating system; hard disk with at least 12.7 MB free space. 

This database will run on Windows 7  using the Windows XP Mode – Virtual PC. 

This database is not compatible with 64 Bit systems.

Please click here to view the PDF version of Users' Guide.

For more information please contact:

Standard Reference Data Program
National Institute of Standards and Technology
100 Bureau Dr., Stop 8553
Gaithersburg, MD 20899-2310
(844) 374-0183 (Toll Free)/ (301) 975-4553 (FAX)Contact Us

The scientific contact for this database is:

Don Burgess
National Institute of Standards and Technology
100 Bureau Dr., Stop 8320
Gaithersburg, MD 20899-2310
E- Mail donald.burgess [at] (donald[dot]burgess[at]nist[dot]gov)


Keywords: Acidity constants, aqueous solutions, compilation equilibrium constants, critical stability constants, dissociation constants, enthalpies, enthalpy, entropy, formation constants, formation equilibria, formation equilibrium, ionic strength, ligands, metal complexes, protonation constants, stability constants, thermochemistry, thermodynamic parameters, thermodynamics.

Created January 29, 2013, Updated October 28, 2019