NIST Standard Reference Database 46

NIST Critically Selected Stability 

Constants of Metal Complexes Database 

Version 8.0 For Windows 

Users' Guide 

Data collected and selected by: 

R. M. Smith and A. E. Martell 

Program developed by: 

R. J. Motekaitis 

Texas A&M University

College Station, TX 77843-3255 

May 2004 

U.S. Department of Commerce 

Technology Administration 

National Institute of Standards and Technology

Standard Reference Data Program 

Gaithersburg, MD 20899 
The National Institute of Standards and Technology (NIST) uses its 

best efforts to deliver a high quality copy of the database and to

verify that the data contained therein have been selected on the basis 

of sound scientific judgment. However, NIST makes no warranties to 

that effect, and NIST shall not be liable for any damage that may

result from errors or omissions in the database. 

c) 1993, 1995, 1996, 1997, 1998, 2001, 2003, 2004 copyright by the U.S. 

Secretary of Commerce on behalf of the United States of America. All rights 

reserved. No part of this database may be reproduced, stored in a retrieval 

system, or transmitted, in any form or by any means, electronic, mechanical, 

photocopying, recording, or otherwise, without the prior written permission of 

the distributor. 

MS-DOS, Microsoft, Windows, and Windows NT are registered trademarks of 

Microsoft Corporation. Epson is a registered trademark of Epson America, Inc. 

DeskJet and LaserJet are registered trademarks of Hewlett-Packard Company.

All other brand and product names are trademarks or registered trademarks of 

their respective companies. 
ACKNOWLEDGMENTS

The authors would like to express their sincere appreciation to 

Professors Reed M. Izatt of Brigham Young University, Provo, Utah, 

and Wesley Harris of the University of Missouri, St. Louis, for 

graciously agreeing to test Version 1.0 of the database. In addition, 

thanks also goes to Dr. Robert D. Hancock of Power Engineering, 

Salt Lake City, Utah, who tested Version 2.0 of the database and to 

Dr. Mysore S. Mohan of the Department of Chemistry at Texas A&M 

University for his review of Version 3.0 of the database and in 

particular for pointing out certain corrections to the bibliography. 

The search-by-metal and search-by-author features have been added 

in response to the customer form requests. Many corrections were 

pointed out through e-mail by database users too numerous to 

mention. We encourage users to continue such editorial 

communications. 

The authors are grateful to Extension Specialist Paul Sittler of Texas 

A&M University for the donation of a copy of a personal program 

designed for the instant sorting of thousands of items. Finally, 

gratitude is expressed to all the students and postdoctoral 

researchers who have offered helpful suggestions throughout this 

project. 

TABLE OF CONTENTS

INTRODUCTION.................................................................................1 

SYSTEM REQUIREMENTS ...............................................................2 

INFORMATION IN THE DATABASE..................................................3 

INSTALLATION..................................................................................6 

USE OF THE DATABASE..................................................................8 

A. Starting and Stopping.................................................................8 

B. Help Menus ..................................................................................8 

C. Ligand Searching by Name ........................................................9 

D. Ligand Searching by Formula.................................................. 10 

E. Searching for Ligands Sequentially ........................................ 11 

 Table of Optional Parameters for the Browse Command ...... 12 

F. Searching for a Ligand and a Metal ......................................... 13 

G. Searching the Literature ...........................................................14 

H. Display Window Summary........................................................ 15 

GETTING STARTED ........................................................................ 17 

Appendix A. SELECTION CRITERIA................................................... 19 

A. Outline of Criteria..................................................... 19 

B. Presentation Conventions....................................... 20 

C. Minimum Requirements for Equilibrium Data ....... 21 

D. References................................................................ 21 

Appendix B. CONTACTS ..................................................................... 22 

INTRODUCTION

The NIST Critically Selected Stability Constants of Metal Complexes 

Database is a reference work covering a tremendous number of 

interactions for aqueous systems of organic and inorganic ligands with 

protons and various metal ions. Over 18,000 papers have been examined, 

representing over 99,000 metal-ligand systems, and only data which meet 

the criterion of well-documented, careful work were considered for 

inclusion. Furthermore, the data were scrutinized for consistency by

comparison both with the same systems by different authors and with 

similar systems. All data included herein have met these selection 

guidelines. Bibliographic citations are linked to each ligand-proton or 

ligand-metal combination retrieved. 

The informational scope of the NIST Critically Selected Stability Constants 

of Metal Complexes Database is very similar to that of the six-volume set 

by Martell and Smith (Critical Stability Constants, Plenum Press, New

York, London 1974, 1975, 1977, 1976, 1982 and 1989) except that most of 

the data have been rescrutinized, errors corrected, and some 50% new

material has been added, effectively superseding the values found in the 

published hardbound volumes. 

22,898 protonation constants under specified conditions of temperature 

and ionic strength for over 4,700 ligands, are given. In addition, 3429 heats 

of protonation and 3016 entropies of protonation are also given from data 

provided in the original literature. 

Most of these ligands have been investigated with all sorts of metal ions, 

and hence the stability constants and thermodynamic constants reported 

herein constitute the largest part of the over 99,000 pieces of data. The 

interactions of metal ions with ligands usually result in a large number of 

chemically distinct species. Thus, in addition to the ordinary stability

constants, all other constants have been extracted from the literature to 

give the complete thermodynamic equilibrium descriptions of the systems 

in question. There are 49,447 equilibrium constants as well as 7,577 heats 

of reactions and 6,519 entropies for metal ions other than hydrogen. 

Additionally, there are 1357 ligands included which did not meet the criteria 

of selection. For these, the metal ions studied and the bibliographic 

citations are included, but not the data. These constitute 970 protonation 

studies and 10,560 metal ion studies for which constants were not 

abstracted but complete literature references are given. 

The NIST Critically Selected Stability Constants of Metal Complexes 

Database is an important tool for quickly locating a needed equilibrium 

constant or associated heat of reaction with complete references. Every

 

METAL COMPLEXES 1 
abstracted ligand possesses a structural formula for quick identification. 

Therefore the program is very easy to use. The data are critically selected, 

so that the values chosen are the most reliable. 

The Version 8.0 of the database is now a Windows application. It should 

be easier to use for most Users. Yet, an effort was made to maintain the 

efficient "look and feel" and color schemes of the original Versions 1.0 - 

5.0, so the previous users would not be distracted by having to learn a new

interface. 

 SYSTEM REQUIREMENTS 

a. 80486 PC or greater with Windows® 98, NT, 2000, ME or XP 

b. Hard disk with at least 37 MB free space 

c. Color monitor, VGA or greater 

d. Optional printer: any 80 column printer supported by the operating 

system 

e. CD-ROM drive for installation 

 METAL COMPLEXES 2
INFORMATION IN THE DATABASE

The term "ligand" is used below to refer to any specific organic or inorganic 

complexor, chelator, molecule, ion, anion, base, zwitterion, charge-transfer 

complexor, precipitant, etc. The term "metal" is used synonymously with 

H+

, Mn+, RnH(4-n)N+, B(OH)3, and others. 

The heart of this database is the stability constants, enthalpies and the 

entropies of proton and metal ion equilibria with ligands in aqueous solution 

under defined conditions of ionic strength and temperature. The data is 

critically scrutinized for accuracy and consistency, but all authors are 

identified for a given ligand-metal study without association of a particular 

author with a particular constant. 

Therefore, the search for equilibrium constants in this Database is 

achieved by looking for a desired Ligand with a desired metal. This search 

can be done by 1) Ligand name or name parts; 2) by formula; 3) by

combination of these; and 3) by browsing the database sequentially. A 

further searching refinement is possible by "locking on" to the desired 

metal or metal oxidation state in all of the above searches. Most people 

restrict their searches by Ligand Name parts. 

The yellow opening window menu bar has four active commands: 

The bottom of this window has seven initially inactive command buttons: 

These activate as necessary after a ligand or data are shown. 

To locate a ligand, use the Search command on the menu bar followed by

Ligand, Formula or Browse. These three open an appropriate dialog box 

where search parameters are entered. These search actions show one 

ligand at a time meeting the search criteria. 

 

METAL COMPLEXES 3 
The black window shows a serial number, a formula, the type of ligand, its 

name, and a structural formula. For those ligands that do not meet the 

critical selection criteria, this window shows only the serial number, name 

and a box indicating that "Published data do not meet the criteria for critical 

selection" 

The bottom left most three-command buttons are now active for navigating 

the Next or Previous ligand. When the desired ligand is displayed, its data 

may be shown by clicking on the Data command button. 

The metal-ligand data and optional bibliographic information for each 

ligand metal system are shown on one of two standard data displays: a 

BLUE equilibrium-constant-values display or a RED thermodynamicconstant-values (∆H° and ∆S°) display. The standard data display turns 

GREEN for those ligands and metal ions for which critical constants are 

not given. However, the metals studied are shown, and their bibliography is 

accessible. 

Each BLUE stability constant data display shows the following information: 

a. empirical chemical formula 

b. type of ligand, e.g. H4L 

c. full chemical name(s) with structural formula 

d. metal ion 

e. equilibrium quotient 

 METAL COMPLEXES 4
f. logarithm of the equilibrium constant (range of agreement among 

different papers) 

g. temperature 

h. ionic strength 

i. footnotes (if any) 

j. The top line: internal record number, the record number being 

displayed, and final record number with this ligand. These are 

useful for reporting problems. 

Each RED thermodynamics constant data display has the following 

information: 

a. empirical chemical formula 

b. type of ligand, e.g. H4L 

c. full chemical name(s) with structural formula 

d. metal ion 

e. equilibrium quotient 

f. ∆H or ∆S [Joules and calories listed] (range of agreement among 

different papers) 

g. temperature 

h. ionic strength 

i. footnotes (if any) 

The top line: internal record number, the record number being 

displayed, and final record number with this ligand. These are 

useful for reporting problems. 

Each GREEN non-critical display has the following information: 

a. full chemical name 

b. box with text, “Published data do not meet the criteria for critical 

selection” 

c metal ion 

d. footnote, “The non-critical data may be found in the reference.” 

e. temperature headers and ionic strength headers (empty) 

f. The top line: internal record number, the record number being 

displayed, and final record number with this ligand. These are 

useful for reporting problems. 

Whenever there is more than one page of data with a given ligand, the 

next page can be accessed by clicking on the More command button. 

 

METAL COMPLEXES 5 
The Print Data command is available under File command of the menu 

bar. It offers to print all of the data with this ligand. To print only data with a 

particular metal, use the Metal command button to choose that metal first. 

The Metal command button is available whenever data is displayed. It 

opens a dialog box to limit data display to only that metal. 

The Bibliography command button displays complete bibliography for the 

currently displayed metal-ligand combination. 

The Print Bibliography command is available under File command of the 

menu bar. 

The Footnotes command button displays any footnotes that may be 

present in the data. 

It is possible to find ligands which contain data with a certain metal or 

oxidation state. Click on the Metal command in the Search found on the 

menu bar. A dialog will open to first specify the metal element, which leads 

to a dialog to choose the particular oxidation state. Subsequent ligand 

searches then retrieve only ligands that contain this metal among its data 

listing. 

The database bibliography can be searched directly from the Author 

command found on the menu bar under Search. It is an added 

feature and is unrelated to the search for data. The dialog box 

provides for searching the literature citations by Author with a 

combination of any other part of anticipated references such as 

publication year, journal abbreviation and page numbers. 

For each hit, the yellow display has a complete reference followed by

each ligand studied and a list of metals studied with each ligand. 

INSTALLATION

Place the CD-ROM in the CD drive. In Windows 98, 2000, NT, Me or XP 

Start the installation by either double-clicking on the install file SETUP.EXE 

on the CD via the Windows Explorer or My Computer, or by clicking on the 

Start button, selecting Run and entering the appropriate location for the 

installation file e.g. D:\SETUP.EXE (if the CD-ROM drive is assigned the 

letter D:). 

 METAL COMPLEXES 6

Follow the remainder of the Installation instructions. 
If you have downloaded the version with source code from web, it will be 

installed by default. Otherwise the code will not be installed, but can be 

copied off of the accompanying CD-ROM. 

To start the program, go to the start button, Programs, NIST, and click on 

critical. 

A NIST Metal Complexes Database Program Group will be created at the 

end of the installation. 

After installation, the following 34 files should be present for the program to 

function properly. In addition, there should be 7 files with DLL extension 

and 6 OCX files and a User Guide.DOC. The program does not create or 

use any other files: 

BIB.DAT CODE4.DAT LMBIB.DAT

BINV3.DAT CODE5.DAT MASTER.STR

BPOINTER.DAT CODE6.DAT OVERFLOW.WDS

CODE1.DAT CRITICAL.EXE POINTER.DAT

CODE2.DAT INV3.DAT REFNUMB.DAT

CODE3.DAT LIGNUMB.DAT VALUES.DAT

USER GUIDE.DOC 

 

METAL COMPLEXES 7 
USE OF THE DATABASE

A. STARTING AND STOPPING 

To run the database from Windows environment double click on the 

program icon. 

You may exit the program any time by clicking Exit (File menu). 

B. HELP MENUS 

The Help menu has 5 submenus: 

Help: 

details of all commands with examples 

General Instructions: 

highly abbreviated highlights to help searching 

Disclaimer: 

 legal statement 

Specifications: 

 database contents 

About: 

Authors and e-mail contacts 

 METAL COMPLEXES 8
C. LIGAND SEARCHING BY NAME 

Note: All ligand names in the database start with a capitalized first letter 

and continue with lower-case letters. 

The Ligand search command (Search menu) provides a dialog box asking 

for "LIGAND SEARCH WORDS?" 

One can search either for a specific ligand name or for all ligands or 

indexes that contain a specific string of characters. The search keys typed 

here are intrinsically upper-case and lower-case sensitive. All ligand names 

in the database start with a capitalized first letter and continue with 

lower-case letters. Thus "Glycine" and "glycine" will find different sets of 

ligands. To do a case-insensitive search uses all capital letters only. Thus 

"GLYCINE" will pick up all Glycines and glycines. 

Keeping the above in mind, here are the rules: 

1. A single search word must have at least 3 consecutive alphabetical 

letters. 

2. Two or more search words are separated by a space. 

3. Commas cannot be used as word separators. Use only spaces. 

4. When more than one search word is used, rule 1 applies only to 

one of the words. Other search words can be brackets, Greek 

letters spelled out, primes, semicolons, numbers, braces... 

5. Any name fragment can be used. To find "Cyclohexylamine", one 

may type, in the LIGAND SEARCH WORDS dialog box: 

a. Cyclohexylamine 

b. CYCLOHEXYLAMINE 

c. yclo amin 

d. CYCLO AMINE 

e. amine yclo hexyl

f. AMINE C6 N1 

Response a. will find Cyclohexylamine unequivocally. 

 

METAL COMPLEXES 9 
Response b. will find Cyclohexylamine first, but further paging will 

show additional hits such as Dicyclohexylamine and 

N,N-Dimethylcyclohexylamine. This case-insensitive string search 

was initiated by using all capital letters. 

Response c. finds about 61 matching names (such as 

trans-1,2-Cyclohexylenediiminodipropanedioic acid and 

1,5-diazacyclooctane-N,N'-diacetic acid) before stepping to 

Cyclohexylamine. All compounds are cyclic amines and were found 

because their names contain the word fragment "yclo" and their 

indexes contain the fragment "amin". 

Response d. finds hits Cyclopropylamine, 

Cyclopentylamine, Cyclohexylamine (the desired ligand), 

Cyclohexylmethylamine,Tricyclo[3.1.1.1(3,7)]decan-1-amine,... 

Each ligand found has an upper or lower case "cyclo" and "amine" 

in its name. This case-insensitive string search was initiated by

using all capital letters. 

Response e. illustrates that the order in which the word fragments 

are entered is immaterial. For this combination Cyclohexylamine is 

found immediately. There are other matches. 

Response f. is an example whereby a case-insensitive (all caps) 

amine containing six carbon atoms and one nitrogen is sought. 

There are 16 hits, but Cyclohexylamine comes up second. If the "1" 

were left off, a redundant all-nitrogen-containing ligand search 

would be made, and many more unwanted hits would result. 

The initial setting for this Ligand search words dialog box is set for 

(EDTA) as the initial default search word. Many common acronyms 

in the database are surrounded by ( ). Try (NTA) vs. NTA. 

D. LIGAND SEARCHING BY FORMULA

The Formula command (Search menu) brings up a formula dialog box 

which allows direct ligand search by empirical formula. This dialog box 

looks very similar to the previous by-name dialog box. "Formula" is one or 

more terms separated by spaces. Each formula term is case sensitive and 

 METAL COMPLEXES 10
often consists of an element symbol followed by a fused multiplier. 

However formula terms may be anything expected in the sought ligand’s 

name. Examples: 

a. C12 H22 O11 

b. O11 C12 H22 

c. N4 

d. N4 PYRID 

e. 3,3,4 

f. H3 P1 O4 

g. [14] 

h. [14] O3 

Response a,b. These examples illustrate the most common usage 

of the FORMULA command and will locate Sucrose and several 

other disaccharides regardless of ordering if space delimited. 

Response c. Will locate any 4 nitrogen ligand. 

Response d. Will locate a 4 nitrogen pyridine derivative. It may also 

find a compound such as [14]aneN4 with a higher than 4 N count. 

Response e. Will locate 3,3,4-Tet (thermospermine or 1,5,9,14-

tetraazatetradecane.) 

Response f. Will find phosphoric acid, but not as a first hit. 

Response g. Will find all 14-membered macrocyclic ring containing 

ligands. 

Response h. Will find all 14-membered macrocyclic ring ligands 

with 3 oxygens in the ligand. The oxygens are not necessarily in the 

ring. 

E. SEARCHING FOR LIGANDS SEQUENTIALLY 

The BROWSE command (Search menu) is useful for sequential paging 

forward (Next command) and backward (Previous command) through 

groups of similar ligands. The optional parameter N for the dialog box is 

the serial number of the ligand on which browsing starts. Without the 

parameter the browsing starts at the last ligand displayed. The ligands 

N≤4708 are the main body for which numeric data are available. 

Ligands>4708 are "Other Ligands" for which the metals studied and 

bibliography has been compiled, but no data are included. The largest 

allowed BROWS parameter is 6166. (There is no Ligand #1) 

 

METAL COMPLEXES 11 
The Table at the end of this section lists other broad values of the browse 

N parameter. Examples of this parameter are: 

a. 2 

b. 683 

c. 4810 

Response a. Starts BROWSE at the first ligand. (There is no ligand 1. 

The 1st record is reserved for internal file information.) 

Response b. Starts Browse at ligand 683, Diglycine, the first of the 

peptide ligands for which critical data were compiled. 

Response c. Starts browse at ligand 4810, at the beginning of "other 

ligands" cis-2-Aminocyclohexanecarboxylic acid. 

Response d. No parameter was entered therefore the last ligand 

displayed becomes available as starting point for browsing either 

forward (Next) or backward (Previous). 

Table of Optional Parameters for the 

Browse Command (Search Menu) 

CRITICALLY SELECTED LIGANDS (blue and red data windows) 

2 Amino Acids 

181 secondary N 

286 tertiary N 

335 Aza macrocycles with carboxylic acids 

425 Iminodiacetic acid and derivatives 

463 NTA and derivatives 

574 EDTA and derivatives 

683 Peptides 

875 tripeptides 

961 polypeptides 

1110 Aniline carboxylic acids 

1187 Pyridine carboxylic acids 

1228 Aliphatic amines 

1565 secondary N 

1718 tertiary N 

1825 Cyclic amines 

1877 Aza-macrocycles 

2051 oxa 

2172 oxo 

2249 thia 

2277 Pyrroles (azoles) 

2418 Pyridines (azines) 

 METAL COMPLEXES 12
2655 Quinolines 

2687 Bipyridines 

2721 Phenanthrolines 

2734 Tripyridines 

2754 Pyrimidines 

2802 Purines 

2856 phosphates 

2890 Aminophosphorus acids 

3042 Carboxylic acids 

3219 hydroxy

3280 keto 

3321 oxy

3366 thio 

3473 diacids 

3553 hydroxy

3651 polyacids 

3705 Organophosphorus and arsenic acids 

3806 Phenols 

3871 salicylic acids 

3946 Catechols 

3995 fuchsons 

4031 Naphthols 

4131 Ketones (oxo ligands) 

4175 cyclic 

 Miscellaneous ligands 

4231 alcohols and sugars 

4285 crown ethers 

4313 sulfides 

4346 mercaptans 

4391 hydrocarbons 

4482 sulfonic acids 

4498 hydroxamic acids 

4577 amides 

4635 ureas, hydrazides, amidines 

4708 Inorganic ligands 

LIGANDS NOT SELECTED (green data windows only)

4810 First Ligand 

6166 Last Ligand 

__________________________________________________________ 

F. SEARCHING FOR LIGAND WITH A METAL 

There is no direct way to search for a metal ion. This would be impractical, 

since most metal ions appear too often. Instead, with the Metal command 

(Search menu) a dialog is established to specify the metal element (case 

sensitive) and metal oxidation states (case sensitive) of interest. The 

choice of metal is then locked on so that any

 

METAL COMPLEXES 13 
Ligand, Formula, or Browse will show ligand matches containing the 

specified metal ion. A large information box is shown to remind the user 

which metal ion is specified from the displayed table. To select a species, 

type the species exactly. To select all the metal species with a given metal, 

simply click OK. These queries are case-sensitive, e.g. Fe works, FE or fe 

does not work. 

G. SEARCHING THE LITERATURE 

The Author command (Search menu) starts a case-sensitive, binary

indexed, chronological search for bibliographic information based on 

author’s names entered into the search dialog box. Enter words, names, 

numbers, etc. separated by a space. If a match is found, the citation is 

shown with the ligands and metals studied. Examples: 

a. Smith 

b. smith 

c. SMITH 

d. mit 

e. mann 

f. Mann 

g. Schwarzen 1947 Acker 

h. Martell 198 

i. bach G. 

Response a. Will find the first occurrence of Smith with an option to 

continue searching for more references. It will also locate Smithson. 

Response b. Because the first letter is not capitalized, no hits are 

possible except in the middle of some name. 

Response c. No hits possible because all caps. This is not to be 

confused with the case insensitivity obtained by capitalizing the entire 

query on the Ligand Search command 

Response d. Smith will be found first, but that is lucky. 

Response e. Shumann will be found first, but not Mann. 

 METAL COMPLEXES 14
Response f. Mannweiler will be found first. 

Response g. Typical suggested query, in this case one is looking for a 

paper by Schwarzenbach and Ackerman published in 1947. Order of 

words is unimportant. Here’s the first reference found: 

Response h. A suggestion to find all papers published by A.E. Martell 

in the 80's. 

Response i. A suggestion to find Gerald Schwarzenbach if you are 

unsure of the spelling. 

H. DISPLAY WINDOW SUMMARY 

All stability and thermodynamic constant data are shown directly on the 

data display window. In addition, the bibliographic data can be accessed 

from these windows. Each window can take on one of three colors: BLUE, 

RED or GREEN. For a given ligand pressing Data button originally

accesses this window. 

1. BLUE DATA WINDOW is the usual stability constant display. The values 

listed are always presented as logarithms of quotients shown. For each 

ligand the highest protonation constant is listed on the first page. When 

data are available under several conditions, the values at 0.100 ionic 

strength are listed first and those at 0 are listed last. 

2. RED DATA WINDOW is the thermodynamic constant display. The ∆H 

values are given in both kcal/mol and kJ/mol together with the defining 

quotient, and on a subsequent page the calculated ∆S values are given in 

cal/deg/mole and J/deg/mole. 

 

METAL COMPLEXES 15 
3. GREEN WINDOW allows quick realization that the ligand or metal ion 

has no critical data associated with it. However, the metals studied with this 

ligand are shown. The bibliographic information of the non-critical studies is 

also in the database. For example, the ligand 4-nitrophenylazocatechol is a 

ligand for which there are no critical data. 

The data fields are marked by a star symbol (*) for the non critical 

metal/ligand combinations. 

Common to all three data display windows are the following commands: 

Data Handling (Command buttons) 

a. More Lists next page of data records 

b. Metal Jump and lock onto particular ion 

unlocks ion when nothing is entered 

c. Bibliography Bibliography displayed 

d. Footnotes Footnotes displayed (if any) 

Printing Commands (File menu) 

e. Print Data Print data with displayed ligand 

Print data with displayed metal (see b. Metal) 

f. Print Bibliography Print reference of displayed metal 

Resume search Commands 

g. Next Next Ligand (button) 

h. Previous Search in opposite direction (button) 

i. Help Help (menu bar) 

j. Exit Quit the program (File menu) 

 METAL COMPLEXES 16
GETTING STARTED

Install the program on the hard disk according to the directions. Then 

double click icon to start the program and read the opening window which 

contain useful and legal information. 

On the menu bar, click Help and read the items in reverse order: 

About, 

Specifications 

Disclaimer 

Generic Instructions: Study this abbreviated summary carefully

Help: Scroll through for future reference of all details. 

On the menu bar, click Search then Author: 

(This will not find any constants, but allows studying the bibliography) 

Enter some author names or parts of names. One of the parts must be 

longer than literal characters. Note the case sensitive search. 

Try the above examples on page 15: “G. Searching the Literature.” 

On the menu bar, click Search then Ligand. 

In the dialog box (EDTA) appears as a default. Click OK. A black 

window with the EDTA structural formula appears. Clicking the 

command button Next indicates that no more (EDTA)'s are in the 

database. Click on the button Data to view a page of log protonation 

constant for EDTA. Click on the button More to see a red page of heats 

corresponding to the first protonation constant. Click on the button 

More again to see a red page of entropies for the first protonation 

equilibrium. Click on More again to see the page of log second 

protonation constant. 

Click the button Metal to see the menu of metals studied with EDTA. 

Type Fe/2, click OK and see ferrous stability constants with EDTA. 

Click on Metal and this time enter Fe/3 and view the ferric EDTA

complexes. 

Try clicking on the Bibliography button. This will display the references 

to the displayed ligand/metal pair. 

Click on the Footnotes button to see any footnotes. 

On the menu bar choose the command Print Data (File menu) and OK the 

selection. Inspect the printed matter. 

On the menu bar choose the command Print Bibliography (File menu) and 

OK the selection. Inspect the printed matter. 

On the menu bar, click on Browse (Search menu). 

This should show a black EDTA window, if that was the last displayed 

ligand. Click the button Next a few times to see various EDTA analogs 

 

METAL COMPLEXES 17 
displayed in succession. Click the button Previous a few times to revisit 

the scrolled by ligands in backward order. If you want, you may

examine any data by clicking the button Data. 

On the menu bar click on Ligand (Search menu). 

Try each of the following and with the button Next inspect the various 

hits as they come up: 

a. Glycine 

b. glycine 

c. ane [ ] C20 

d. Cyclo amine ene 

e. amine N' N'' (two single apostrophes) 

f. ulfur 

g. osph 

h. osph C6 

i. S P C N acid 

On the menu bar, click on Formula (Search menu). 

Try the following formulas and with the button Next inspect the various 

hits as they come up: 

a. C8 

b. C8 N4 

c. N4 C8 

d. Cl2 

e. C7 N1 

On the menu bar, click on Metal (Search menu). 

We will look for any catechol ligand with aluminum constants. From the 

displayed elements block, type in Al (case sensitive). At the species 

menu type in Al or simply click OK to select all of the Al species. Now

click on Browse (Search menu) and type in a parameter like 3580 

(catechols, from table in Help (Help menu)). 

Try all the commands to become familiar with the mechanics of data 

display and metal selection. 

 METAL COMPLEXES 18
Appendix A 

 SELECTION CRITERIA

A. OUTLINE OF CRITERIA1

When several workers are in close agreement on a particular value, the 

average of their results has been selected for that value. Values showing 

considerable scatter have been eliminated. In cases where the agreement 

is poor and few results are available for comparison, more subtle methods 

were needed to select the best value. This selection was often guided by a 

comparison with values obtained for other metal ions with the same ligand 

and with values obtained for the same metal ion with similar ligands. 

While established trends among similar metal ions and among similar 

ligands were valuable in deciding between widely varying values, such 

guidelines were used cautiously, so as not to overlook occasionally

unexpected real examples of specificity or anomalous behavior. 

When there was poor agreement among published values and comparison 

with other metal ions and ligands did not suggest the best value, the 

results of more experienced research groups who had supplied reliable 

values for other ligands were selected. When such assurances were 

lacking, it was sometimes possible to give preference to values reported by

an investigator who had published other demonstrably reliable values 

obtained by the same experimental method. 

Values reported by only one investigator are included in these tables 

unless there was some reason to doubt their validity. It is recognized that 

some of these values may be in error, and that such errors will probably

not be detected until the work is repeated by other investigators. Some 

values have been omitted because of serious questions about the 

composition of their complexes, and the formulation of the equilibrium 

quotients. 

A bibliography for each ligand is included so that the user may determine 

the completeness of the literature search employed in the determination of 

critical values. The user may also employ these references to make his or 

her own evaluation if he or she has any questions or reservations 

concerning this compilation. 

 

METAL COMPLEXES 19 
Papers deficient in specifying essential reaction conditions (e.g., 

temperature, ionic strength, nature of supporting electrolyte) were not 

employed in this compilation. Also used as a basis for disqualification of 

published data is lack of information on the purity of the ligand. Frequent 

deficiencies are lack of calibration of potentiometric apparatus, and failure 

to define the equilibrium quotients reported in the paper. Papers in which 

both temperature and ionic strength are not controlled have been omitted 

from the bibliography. 

B. PRESENTATION CONVENTIONS

The values in the database are considered to be the most reliable of the 

ones available. Values considered to be of questionable validity are 

enclosed in parentheses. Values having considerable doubt have been 

omitted. 

The range of other values considered reliable is given by + or- quantities in 

parentheses, describing the difference in the last digit between the other 

values and the selected value. The range ±0 indicates one or more values 

which agree exactly with the stated value. Ranges above ±10 are rounded 

to the nearest ten. Uncertainties of the numbers in the database are 

indicated by the number of significant figures employed. The larger the 

numbers of significant figures, the more reliable are the numbers in the 

database. 

All equilibria are expressed as concentration constants. Mixed protonation 

constants were converted to concentration constants using hydrogen ion 

activity coefficients. Protonation constants determined at pH values above 

12 or below 2 are questioned because of their reduced accuracy. 

Enthalphy values determined from temperature variation are also 

questioned. Data set in parentheses represents the questioned values. 

Equilibrium constants are given for 25°C unless other temperatures were 

used and an enthalphy value was not available for conversion to 25°C. 

Equilibrium data in the database are listed to the nearest 0° or 5° except 

for 12°, 18°, 22°, 27°, and 37°. Values at 37° and 0.15 ionic strength are 

included where available. Temperature ranges for enthalphy calculations 

from temperature variation are rounded to the nearest ten. 

Equilibrium data in the database are listed at the most commonly used 

values of ionic strength: 0.1, 0.5, 0.7, 1.0, 2.0, 3.0, etc. Thus 0.1 

represents values from 0.05 to 0.24 and 0.5 include those from 0.25 to 

0.60. 

 METAL COMPLEXES 20
Log K values at ionic strengths greater than zero and less than 0.05 are 

not used. 

C. MINIMUM REQUIREMENTS FOR EQUILIBRIUM DATA2,3

1. The equilibrium quotients and each term in the equilibrium quotient 

should be carefully defined. 

2. The purity of ligands, reagents and solvents, and the procedures 

followed in their purification must be described. 

3. The ionic strength, the composition of the solution, and other 

relevant factors including the range of metal and ligand 

concentrations investigated must be included. 

4. The pH range over which measurements have been made, the 

titrant used, and the Kw value used must be stated. 

5. The pH meter, electrode, and other instruments such as 

spectrophotometer, etc., used in the experimental studies and an 

explicit description of the method of calibration must be described. 

6. The temperature and temperature range must be stated. 

7. The number of data points used per titration (or elsewhere as 

appropriate), and the number of replicate measurements must be 

recorded. 

8. The computer program, or the method of calculation used to derive 

the results from experimental values must be included. Previously

unpublished programs and calculation procedures should be 

described in terms of the stepwise logic involved. 

9. The final results should include the range together with the standard 

deviation, the sources of error, and the methods used in 

establishing parameters. 

10. The assumptions made in working up and modeling the data as well 

as any problems encountered during the determinations or 

calculations should be clearly set forth. 

D. REFERENCES

1. Martell, A. E.; R. M. Smith, Critical Stability Constants, Vols. 1-6, 

Plenum Press, New York, 1974, 1975, 1977, 1976, 1982, 1989. 

2. Tuck, D. G. Pure Appl. Chem. 1989, 61, 1161. 

3. Martell, A. E.; Motekaitis, R. J., The Determination and Use of 

Stability Constants, 2nd Edition, VCH Publishers, Deerfield Beach, 

FL, 1992. 

 

METAL COMPLEXES 21 
 METAL COMPLEXES 22

Appendix B CONTACTS 

If you wish to contact the Texas A&M authors of the Stability Constant 

Database: 

Texas A&M University 

Department of Chemistry 

College Station TX 77843-3255 

Data Collection and Selection: 

Robert M. Smith 

rsmith@mail.chem.tamu.edu 

NOTE: The author would appreciate an e-mail of errors found. 

Indicate the Ligand by number and the nature of the error found. 

Ex.:#694 The name should be Picolyl-L-histidine. 

1. Indicate the page by providing the three internal index 

numbers. 

Ex.: The bibliography on screen 59426 59427 

59478 is missing a reference to our work. 

J. L. Messer and B.T. Wasser, J. Kin. Meas. 1987, 

20, p 199-201. 

2. Indicate AUTHOR screens by providing the 

bibliographic symbol. 

3. Ex.: In Reference 53RQa there is no mention of H. Only 

metals are given. 

If you have questions or comments about the database, Standard 

Reference Data would like to hear from you. Also, if you have any 

problems with the diskettes or installation, please let us know by 

contacting: 

Joan Sauerwein 

National Institute of Standards and Technology 

Standard Reference Data Program 

Building 820, Room 102, Stop 2310 

Gaithersburg, MD 20899-2310 

FAX: (301) 926-0416 

Phone: (301) 975-2008 

Internet: www.nist.gov/srd