E4a: Stepwise Association Constants

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The following table provides K_i and β_i 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: C₂O₄^2–	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: S₂O₃^2–	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	-	-

Contributors and Attributions

David Harvey (DePauw University)

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