PC Database Offers Rapid Access to Reaction Rates of Ligands in Solutions

NIST Standard Reference Database 46, NIST Critical Stability Constants of Metal Complexes, provides research chemists and chemical engineers with rapid access to important information on the reaction rates of ligands and how they react with ions to form complex chemical compounds. The new personal computer database is available from the National Institute of Standards and Technology.

Ligands are atoms or groups of atoms bound to a central atom. Information on the interactions of ligands with hydrogen and other metal ions in water is of prime concern to many, including mining engineers and geologists; scientists investigating the stability of materials in the environment; chemists developing agricultural fertilizers, pesticides and other products; biologists studying membrane structures; and for manufacturing engineers in the control of various industrial processes such as electroplating and finishing.

The PC database contains data on the interactions in aqueous systems of nearly 4,000 organic and inorganic ligands with protons and various metal ions. The database was developed by Arthur E. Martell, Robert M. Smith and Ramunas J. Motekaitis at Texas A&M; University, with support from the NIST Standard Reference Data Program.

Information in the database is very similar to that in a six-volume reference, Critical Stability Constants by Martell and Smith. To develop the computerized reference tool, the scientists re-examined and critically evaluated all of the information in the printed reference, corrected errors and added new recommended values.

The PC version enables scientists to locate information quickly. For every abstracted ligand, there is a structural formula for quick identification. For each of the nearly 4,000 ligands listed, there are rates for reaction with protons under specified conditions of temperature and ionic strength. The heats of protonation also are included if they were provided in the original literature. Similar information is given for metal ions. There are almost 80,000 data values in the collection with complete references to source.

The database also cites papers that are deficient in specifying the essential reaction conditions of more than 1,000 ligands. The data in these references did not meet the evaluation criteria for the new PC reference. For these studies, the metal ions and the bibliographic citations are included, but not the data.

Since 1968, the NIST Standard Reference Data Program has been providing reliable, well-documented reference data to scientists and engineers for use in technical problem-solving, research and development. Standard reference data have been used to improve design efficiency of chemical processes, to identify potentially toxic substances in the environment, to improve materials durability, and to calculate performance of chemical reactors, to name but a few applications.

NIST Standard Reference Database 46, NIST Critical Stability Constants of Metal Complexes, is available for $240 from the Standard Reference Data Program, A320 Physics Building, NIST, Gaithersburg, Md. 20899-0001, (301) 975-2208, fax: (301) 926- 0416, e-mail: srdata [at] enh.nist.gov (srdata[at]enh[dot]nist[dot]gov) (via Internet). It requires a DOS-based personal computer and at least 6.6 MB of free memory, and an EGA color monitor with greater than 64K memory on the adapter.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.