16.12: Formation Constants

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The following table provides \(K_i\) and \(\beta_i\) values for selected metal–ligand complexes, arranged by the ligand. 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.

Acetate \(\ce{CH3COO-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)
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
Ag⁺	0.73	–0.09
Zn²⁺	1.57
Cd²⁺	1.93	1.22	–0.89
Pb²⁺	2.68	1.40

Ammonia \(\ce{NH3}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_5\)	log \(K_6\)
Ag⁺	3.31	3.91
Co²⁺ (T = 20 °C)	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 \(\ce{Cl-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)
Cu²⁺	0.40
Fe³⁺	1.48	0.65
Ag⁺ (\(\mu = 5.0 \text{ M}\))	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 \(\ce{CN-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_6\)
Fe²⁺					35.4 (\(\beta_6\))
Fe³⁺					43.6 (\(\beta_6\))
Ag⁺		20.48 (\(\beta_2\))	0.92
Zn²⁺		11.07 (\(\beta_2\))	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 (\(\beta_4\))

Ethylenediamine \(\ce{H2NCH2CH2NH2}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)
Ni²⁺	7.38	6.18	4.11
Cu²⁺	10.48	9.07
Ag⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	4.700	3.00
Zn²⁺	5.66	4.98	3.25
Cd²⁺	5.41	4.50	2.78

EDTA	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_5\)	log \(K_6\)
Mg²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	8.79
Ca²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	10.69
Ba²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	7.86
Bi³⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	27.8
Co²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	16.31
Ni²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	18.62
Cu²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	18.80
Cr³⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	[23.4]
Fe³⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	25.1
Ag⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	7.32
Zn²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	16.50
Cd²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	16.46
Hg²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	21.7
Pb²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	18.04
Al³⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	16.3

Fluoride \(\ce{F-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_5\)	log \(K_6\)
Al³⁺	6.11	5.01	3.88	3.0	1.4	0.4

Fluoride

\(\ce{F-}\)

log \(K_1\)

log \(K_2\)

log \(K_3\)

log \(K_4\)

log \(K_5\)

log \(K_6\)

Al³⁺

6.11

5.01

3.88

3.0

1.4

0.4

Hydroxide \(\ce{OH-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)
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 \(\ce{I-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)
Ag⁺	6.58	[5.12]	[1.4]
Cd²⁺ (T = 18 °C)	2.28	1.64	1.08	1.0
Pb²⁺	1.92	1.28	0.7	0.6

Iodide

\(\ce{I-}\)

log \(K_1\)

log \(K_2\)

log \(K_3\)

log \(K_4\)

log \(K_5\)

log \(K_6\)

Ag⁺

6.58

[5.12]

[1.4]

Cd²⁺ (T = 18 °C)

2.28

1.64

1.08

1.0

Pb²⁺

1.92

1.28

0.7

0.6

Nitriloacetate	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_5\)	log \(K_6\)
Mg²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	5.41
Ca²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	6.41
Ba²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	4.82
Mn²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	7.44
Fe²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	8.33
Co²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	10.38
Ni²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	11.53
Cu²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	12.96
Fe³⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	15.9
Zn²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	10.67
Cd²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	9.83
Pb²⁺ (T = 20 °C, \(\mu = 0.1 \text{ M}\))	11.39

Oxalate \(\ce{C2O4^{2-}}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)
Ca²⁺ (\(\mu = 1 \text{ M}\))	1.66	1.03
Fe²⁺ (\(\mu = 1 \text{ M}\))	3.05	2.10
Co²⁺	4.72	2.28
Ni²⁺	5.16
Cu²⁺	6.23	4.04
Fe³⁺ (\(\mu = 0.5 \text{ M}\))	7.53	6.11	4.83
Zn²⁺	4.87	2.78

1,10-phenanthroline	log \(K_1\)	log \(K_2\)	log \(K_3\)
Fe²⁺			20.7 (\(\beta_3\))
Mn²⁺ (\(\mu = 0.1 \text{ M}\))	4.0	3.3	3.0
Cu²⁺ (\(\mu = 0.1 \text{ M}\))	7.08	6.64	6.08
Ni²⁺	8.6	8.1	7.6
Fe³⁺			13.8 (\(\beta_3\))
Ag⁺ (\(\mu = 0.1 \text{ M}\))	5.02	7.04
Zn²⁺	6.2	[5.9]	[5.2]

Thiosulfate \(\ce{S2O3^{2-}}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)	log \(K_5\)	log \(K_6\)
Ag⁺ (T = 20 °C)	8.82	4.85	0.53

Thiosulfate

\(\ce{S2O3^{2-}}\)

log \(K_1\)

log \(K_2\)

log \(K_3\)

log \(K_4\)

log \(K_5\)

log \(K_6\)

Ag⁺ (T = 20 °C)

8.82

4.85

0.53

Thiocyanate \(\ce{SCN-}\)	log \(K_1\)	log \(K_2\)	log \(K_3\)	log \(K_4\)
Mn²⁺	1.23
Fe²⁺	1.31
Co²⁺	1.71
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 (\(\beta_2\))	2.71	1.83