E4a: Stepwise Association Constants
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The following table provides Ki and βi values for selected metal–ligand complexes, arranged by the ligand (red). All values are from Martell, A. E.; Smith, R. M. Critical Stability Constants, Vols. 1–4. Plenum Press: New York, 1976. Unless otherwise stated, values are for 25 oC and zero ionic strength. Those values in brackets are considered less reliable. For more details read here.
Acetate
Acetate \(CH_3COO^{-}\) |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Mg2+ |
1.27 |
- |
- |
- |
- |
- |
Ca2+ |
1.18 |
- |
- |
- |
- |
- |
Ba2+ |
1.07 |
- |
- |
- |
- |
- |
Mn2+ |
1.40 |
- |
- |
- |
- |
- |
Fe2+ |
1.40 |
- |
- |
- |
- |
- |
Co2+ |
1.46 |
- |
- |
- |
- |
- |
Ni2+ |
1.43 |
- |
- |
- |
- |
- |
Cu2+ |
2.22 |
1.41 |
- |
- |
- |
- |
Ag2+ |
0.73 |
–0.09 |
- |
- |
- |
- |
Zn2+ |
1.57 |
- |
- |
- |
- |
- |
Cd2+ |
1.93 |
1.22 |
–0.89 |
- |
- |
- |
Pb2+ |
2.68 |
1.40 |
- |
- |
- |
- |
Ammonia
Ammonia: NH3 |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Ag+ |
3.31 |
3.91 |
- |
- |
- |
- |
Co2+ (T = 20 oC) |
1.99 |
1.51 |
0.93 |
0.64 |
0.06 |
–0.73 |
Ni2+ |
2.72 |
2.17 |
1.66 |
1.12 |
0.67 |
–0.03 |
Cu2+ |
4.04 |
3.43 |
2.80 |
1.48 |
- |
- |
Zn2+ |
2.21 |
2.29 |
2.36 |
2.03 |
- |
- |
Cd2+ |
2.55 |
2.01 |
1.34 |
0.84 |
- |
- |
Chloride
Chloride: Cl– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Cu2+ |
0.40 |
- |
- |
- |
- |
- |
Fe3+ |
1.48 |
0.65 |
- |
- |
- |
- |
Ag+ (μ = 5.0 M) |
3.70 |
1.92 |
0.78 |
–0.3 |
- |
- |
Zn2+ |
0.43 |
0.18 |
–0.11 |
–0.3 |
- |
- |
Cd2+ |
1.98 |
1.62 |
–0.2 |
–0.7 |
- |
- |
Pb2+ |
1.59 |
0.21 |
–0.1 |
–0.3 |
- |
- |
Cyanide
Cyanide: CN– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Fe2+ |
- |
- |
- |
- |
- |
35.4 (β6) |
Fe3+ |
- |
- |
- |
- |
- |
43.6 (β6) |
Ag+ |
- |
20.48 β2 |
0.92 |
- |
- |
- |
Zn2+ |
- |
11.07 β2 |
4.98 |
3.57 |
- |
- |
Cd2+ |
6.01 |
5.11 |
4.53 |
2.27 |
- |
- |
Hg2+ |
17.00 |
15.75 |
3.56 |
2.66 |
- |
- |
Ni2+ |
- |
- |
- |
30.22 (β4) |
- |
- |
Ethylenediamine
Ethylenediamine

|
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Ni2+ |
7.38 |
6.18 |
4.11 |
- |
- |
- |
Cu2+ |
10.48 |
9.07 |
- |
- |
- |
- |
Ag+ (T = 20 oC, μ = 0.1 M) |
4.700 |
3.00 |
- |
- |
- |
- |
Zn2+ |
5.66 |
4.98 |
3.25 |
- |
- |
- |
Cd2+ |
5.41 |
4.50 |
2.78 |
- |
- |
- |
EDTA
EDTA

|
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Mg2+ (T = 20 oC, μ = 0.1 M) |
8.79 |
- |
- |
- |
- |
- |
Ca2+ (T = 20 oC, μ = 0.1 M) |
10.69 |
- |
- |
- |
- |
- |
Ba2+ (T = 20 oC, μ = 0.1 M) |
7.86 |
- |
- |
- |
- |
- |
Bi3+ (T = 20 oC, μ = 0.1 M) |
27.8 |
- |
- |
- |
- |
- |
Co2+ (T = 20 oC, μ = 0.1 M) |
16.31 |
- |
- |
- |
- |
- |
Ni2+ (T = 20 oC, μ = 0.1 M) |
18.62 |
- |
- |
- |
- |
- |
Cu2+ (T = 20 oC, μ = 0.1 M) |
18.80 |
- |
- |
- |
- |
- |
Cr3+ (T = 20 oC, μ = 0.1 M) |
[23.4] |
- |
- |
- |
- |
- |
Fe3+ (T = 20 oC, μ = 0.1 M) |
25.1 |
- |
- |
- |
- |
- |
Ag+ (T = 20 oC, μ = 0.1 M) |
7.32 |
- |
- |
- |
- |
- |
Zn2+ (T = 20 oC, μ = 0.1 M) |
16.50 |
- |
- |
- |
- |
- |
Cd2+ (T = 20 oC, μ = 0.1 M) |
16.46 |
- |
- |
- |
- |
- |
Hg2+ (T = 20 oC, μ = 0.1 M) |
21.7 |
- |
- |
- |
- |
- |
Pb2+ (T = 20 oC, μ = 0.1 M) |
18.04 |
- |
- |
- |
- |
- |
Al3+ (T = 20 oC, μ = 0.1 M) |
16.3 |
- |
- |
- |
- |
- |
Fluoride
Fluoride: F– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Al3+ (μ = 0.5 M) |
6.11 |
5.01 |
3.88 |
3.0 |
1.4 |
0.4 |
Hydroxide
Hydroxide: OH– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Al3+ |
9.01 |
[9.69] |
[8.3] |
6.0 |
- |
- |
Co2+ |
4.3 |
4.1 |
1.3 |
0.5 |
- |
- |
Fe2+ |
4.5 |
[2.9] |
2.6 |
–0.4 |
- |
- |
Fe3+ |
11.81 |
10.5 |
12.1 |
- |
- |
- |
Ni2+ |
4.1 |
3.9 |
3.
|
- |
- |
- |
Pb2+ |
6.3 |
4.6 |
3.0 |
- |
- |
- |
Zn2+ |
5.0 |
[6.1] |
2.5 |
[1.2] |
- |
- |
Iodide
Iodide: I– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Ag+ (T = 18 oC) |
6.58 |
[5.12] |
[1.4] |
- |
- |
- |
Cd2+ |
2.28 |
1.64 |
1.08 |
1.0 |
- |
- |
Pb2+ |
1.92 |
1.28 |
0.7 |
0.6 |
- |
- |
Nitriloacetate
Nitriloacetate
 |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Mg2+ (T = 20 oC, μ = 0.1 M) |
5.41 |
- |
- |
- |
- |
- |
Ca2+ (T = 20 oC, μ = 0.1 M) |
6.41 |
- |
- |
- |
- |
- |
Ba2+ (T = 20 oC, μ = 0.1 M) |
4.82 |
- |
- |
- |
- |
- |
Mn2+ (T = 20 oC, μ = 0.1 M) |
7.44 |
- |
- |
- |
- |
- |
Fe2+ (T = 20 oC, μ = 0.1 M) |
8.33 |
- |
- |
- |
- |
- |
Co2+ (T = 20 oC, μ = 0.1 M) |
10.38 |
- |
- |
- |
- |
- |
Ni2+ (T = 20 oC, μ = 0.1 M) |
11.53 |
- |
- |
- |
- |
- |
Cu2+ (T = 20 oC, μ = 0.1 M) |
12.96 |
- |
- |
- |
- |
- |
Fe3+ (T = 20 oC, μ = 0.1 M) |
15.9 |
- |
- |
- |
- |
- |
Zn2+ (T = 20 oC, μ = 0.1 M) |
10.67 |
- |
- |
- |
- |
- |
Cd2+ (T = 20 oC, μ = 0.1 M) |
9.83 |
- |
- |
- |
- |
- |
Pb2+ (T = 20 oC, μ = 0.1 M) |
11.39 |
- |
- |
- |
- |
- |
Oxalate
Oxalate: C2O42– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Ca2+ (μ = 1 M) |
1.66 |
1.03 |
- |
- |
- |
- |
Fe2+ (μ = 1 M) |
3.05 |
2.10 |
- |
- |
- |
- |
Co2+ |
4.72 |
2.28 |
- |
- |
- |
- |
Ni2+ |
5.16 |
- |
- |
- |
- |
- |
Cu2+ |
6.23 |
4.04 |
- |
- |
- |
- |
Fe3+ (μ = 0.5 M) |
7.53 |
6.11 |
4.85 |
- |
- |
- |
Zn2+ |
4.87 |
2.78 |
- |
- |
- |
- |
1,10-Phenanthroline
1,10-Phenanthroline

|
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Fe2+ |
- |
- |
20.7 (β3) |
- |
- |
- |
Mn2+ (μ = 0.1 M) |
4.0 |
3.3 |
3.0 |
- |
- |
- |
Co2+ (μ = 0.1 M) |
7.08 |
6.64 |
6.08 |
- |
- |
- |
Ni2+ |
8.6 |
8.1 |
7.6 |
- |
- |
- |
Fe3+ |
- |
- |
13.8 (β3) |
- |
- |
- |
Ag+ (μ = 0.1 M) |
5.02 |
7.04 |
- |
- |
- |
- |
Zn2+ |
6.2 |
[5.9] |
[5.2] |
- |
- |
- |
Thiosulfate
Thiosulfate: S2O32– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Ag+ (T = 20 oC) |
8.82 |
4.85 |
0.53 |
- |
- |
- |
Thiocyanate
Thiocyanate: SCN– |
log K1 |
log K2 |
log K3 |
log K4 |
log K5 |
log K6 |
Mn2+ |
1.23 |
- |
- |
- |
- |
- |
Fe2+ |
1.31 |
- |
- |
- |
- |
- |
Co2+ |
1.72 |
- |
- |
- |
- |
- |
Ni2+ |
1.76 |
- |
- |
- |
- |
- |
Cu2+ |
2.33 |
- |
- |
- |
- |
- |
Fe3+ |
3.02 |
- |
- |
- |
- |
- |
Ag+ |
4.8 |
3.43 |
1.27 |
0.2 |
- |
- |
Zn2+ |
1.33 |
0.58 |
0.09 |
–0.4 |
- |
- |
Cd2+ |
1.89 |
0.89 |
0.02 |
–0.5 |
- |
- |
Hg2+ |
- |
17.26 (β2) |
2.71 |
1.83 |
- |
- |
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