Ligand Formation Constants

Source All values are from Martell, A. E. Smith, R. M. Critical Stability Constants, Vol. 1-4, Plenum Press New York, 1976. Unless otherwise stated, values are for 25 °C and zero ionic strength. Values in parentheses are considered less reliable. 

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Conditional Metal—Ligand Formation Constants Recognizing EDTA s acid-base properties is important. The formation constant for CdY in equation 9.11 assumes that EDTA is present as Y . If we restrict the pH to levels greater than 12, then equation 9.11 provides an adequate description of the formation of CdY . for pH levels less than 12, however, K overestimates the stability of the CdY complex. 

A difference plot, also called a Bjerrum plot, is an excellent means to extract metal-ligand formation constants or acid dissociation constants from titration data obtained with electrodes. We will apply the difference plot to an acid-base titration curve. 

The binding constants (illustrated here as metal-ligand formation constants) may be either stepwise formation constants (equation 22-1) or cumulative formation constants Pn (equation 22-2). Charges have been omitted for clarity. 

Since MXY is inherently twice as probable as MX. or MY , statistical considerations alone predict that X 4 ( 1, 3, 5, 5), Accordingly, the statistically modeled mixed ligand formation constant, 6, is given as (1, 3, 5) ... 

Siderophores are highly specific Fe(III) ligands (formation constants often > 10 ) and are excreted by a wide variety of fungi and bacteria to aid iron assimilation because of the low solubility of Fe + at pH values where most life exists. Siderophores are the most common means of acquisition of iron by bacteria and fungi (Crichton, 1991), and in soil, many different species, including plants, will compete for Fe. Although produced primarily as a means of obtaining iron. 

The value of ai will depend on the formation constants of the metal ion-ligand formation constants, the concentration of excess ligand in the mobile phase and the pH. Calculation of Oi according to Ringbom [12] follows the equation ... 

Metal ion-ligand formation constants are listed in Tables 8-2, 9-1, and 9-2. Redox potentials are found in Table 12-1. 

TABLE 8.12 Cumulative Formation Constants for Metal Complexes with Inorganic Ligands... 

In Section 8, the material on solubility constants has been doubled to 550 entries. Sections on proton transfer reactions, including some at various temperatures, formation constants of metal complexes with organic and inorganic ligands, buffer solutions of all types, reference electrodes, indicators, and electrode potentials are retained with some revisions. The material on conductances has been revised and expanded, particularly in the table on limiting equivalent ionic conductances. 

The formation of a metal-ligand complex is described by a formation constant, K. The complexation reaction between Cd + and NH3, for example, has the following equilibrium constant... 

The formation constant for a metal—ligand complex in which only one ligand is added to the metal ion or to a metal—ligand complex Ki). 

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