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preface to fifteenth edition

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8.82 SECTION 8<br />

8.2.2 Formation Constants of Metal Complexes<br />

Each value listed in Tables 8.12 and 8.13 is the logarithm of the overall formation constant for the<br />

cumulative binding of a ligand L <strong>to</strong> the central metal cation M, viz.:<br />

Cumulative<br />

formation constant<br />

Stepwise<br />

stability constants<br />

M L ML K 1 k 1<br />

M 2L ML 2 K 2 k 1 k 2<br />

.................<br />

M nL ML n K n k 1 k 2 ···k n<br />

As an example, the entries in Table 8.12 for the zinc ammine complexes represent these equilibria:<br />

2<br />

[Zn(NH 3) ]<br />

[Zn][NH ]<br />

2<br />

2<br />

Zn NH3 Zn(NH 3) K1 <br />

2<br />

3<br />

2<br />

[Zn(NH 3) 2 ]<br />

2<br />

2<br />

3 3 2 2 2 2<br />

[Zn][NH 3]<br />

Zn 2NH Zn(NH ) K <br />

2<br />

[Zn(NH 3) 3 ]<br />

[Zn][NH ]<br />

2<br />

2<br />

Zn 3NH3 Zn(NH 3) 3 K3 <br />

2 3<br />

3<br />

2<br />

[Zn(NH 3) 4 ]<br />

2<br />

2<br />

Zn 4NH3 Zn(NH 3) 4 K4 <br />

2<br />

[Zn][NH ]<br />

4<br />

3<br />

If the stepwise stability or formation constants of the reactions are desired, for the first step log<br />

K1 log k1<br />

2.37. For the second and succeeding steps the equilibria and corresponding constants<br />

are as follows:<br />

2<br />

2<br />

Zn(NH 3) NH3 Zn(NH 3) 2 log k2 log K2 log K1<br />

2.44<br />

2<br />

2<br />

Zn(NH 3) 2 NH3 Zn(NH 3) 3 log k3 log K3 log K2<br />

3.50<br />

2<br />

2<br />

Zn(NH 3) 3 NH3 Zn(NH 3) 4 log k4 log K4 log K3<br />

2.15<br />

The reverse of the association or formation reactions would represent the dissociation or instability<br />

constant for the systems, i.e., log Kf<br />

log K instab.<br />

The data inthe tables generally refer <strong>to</strong> temperatures of about 20 <strong>to</strong> 25C. Most of the values in<br />

Table 8.12 refer <strong>to</strong> zero ionic strength, but those in Table 8.13 often refer <strong>to</strong> a finite ionic strength.

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