16.12: Formation Constants

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 $K_3$	log $K_4$	log $K_5$	log $K_6$
Mg^2^+	1.27
Ca^2+	1.18
Ba^2^+	1.07
Mn^2^+	1.40
Fe^2+	1.40
Co^2^+	1.46
Ni^2+	1.43
Cu^2^+	2.22	1.41
Ag^+	0.73	–0.09
Zn^2+	1.57
Cd^2^+	1.93	1.22	–0.89
Pb^2+	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
Co^2+ (T = 20 °C)	1.99	1.51	0.93	0.64	0.06	–0.73
Ni^2^+	2.72	2.17	1.66	1.12	0.67	–0.03
Cu^2+	4.04	3.43	2.80	1.48
Zn^2^+	2.21	2.29	2.36	2.03
Cd^2+	2.55	2.01	1.34	0.84

Chloride $\ce{Cl-}$	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Cu^2^+	0.40
Fe^3+	1.48	0.65
Ag^+ ($\mu = 5.0 \text{ M}$)	3.70	1.92	0.78	–0.3
Zn^2^+	0.43	0.18	–0.11	–0.3
Cd^2+	1.98	1.62	–0.2	–0.7
Pb^2^+	1.59	0.21	–0.1	–0.3

Cyanide $\ce{CN-}$	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Fe^2^+						35.4 ($\beta_6$)
Fe^3+						43.6 ($\beta_6$)
Ag^+		20.48 ($\beta_2$)	0.92
Zn^2+		11.07 ($\beta_2$)	4.98	3.57
Cd^2^+	6.01	5.11	4.53	2.27
Hg^2+	17.00	15.75	3.56	2.66
Ni^2^+				30.22 ($\beta_4$)

Ethylenediamine $\ce{H2NCH2CH2NH2}$	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Ni^2^+	7.38	6.18	4.11
Cu^2+	10.48	9.07
Ag^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	4.700	3.00
Zn^2^+	5.66	4.98	3.25
Cd^2+	5.41	4.50	2.78

EDTA	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Mg^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	8.79
Ca^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	10.69
Ba^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	7.86
Bi^3^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	27.8
Co^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	16.31
Ni^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	18.62
Cu^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	18.80
Cr^3^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	[23.4]
Fe^3^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	25.1
Ag^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	7.32
Zn^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	16.50
Cd^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	16.46
Hg^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	21.7
Pb^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	18.04
Al^3^+ (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 $K_6$
Al^3^+	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 $K_4$	log $K_5$	log $K_6$
Al^3^+	9.01	[9.69]	[8.3]	6.0
Co^2^+	4.3	4.1	1.3	0.5
Fe^2+	4.5	]2.9]	2,6	–0.4
Fe^3^+	11.81	10.5	12.1
Ni^2+	4.1	3.9	3.
Pb^2^+	6.3	4.6	3.0
Zn^2+	5.0	[6.1]	2.5	[1.2]

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]
Cd^2+ (T = 18 °C)	2.28	1.64	1.08	1.0
Pb^2^+	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 $K_6$
Mg^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	5.41
Ca^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	6.41
Ba^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	4.82
Mn^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	7.44
Fe^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	8.33
Co^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	10.38
Ni^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	11.53
Cu^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	12.96
Fe^3^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	15.9
Zn^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	10.67
Cd^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	9.83
Pb^2^+ (T = 20 °C, $\mu = 0.1 \text{ M}$)	11.39

Oxalate $\ce{C2O4^{2-}}$	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Ca^2^+ ($\mu = 1 \text{ M}$)	1.66	1.03
Fe^2^+ ($\mu = 1 \text{ M}$)	3.05	2.10
Co^2^+	4.72	2.28
Ni^2^+	5.16
Cu^2^+	6.23	4.04
Fe^3^+ ($\mu = 0.5 \text{ M}$)	7.53	6.11	4.83
Zn^2^+	4.87	2.78

1,10-phenanthroline	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Fe^2^+			20.7 ($\beta_3$)
Mn^2^+ ($\mu = 0.1 \text{ M}$)	4.0	3.3	3.0
Cu^2^+ ($\mu = 0.1 \text{ M}$)	7.08	6.64	6.08
Ni^2^+	8.6	8.1	7.6
Fe^3^+			13.8 ($\beta_3$)
Ag^+ ($\mu = 0.1 \text{ M}$)	5.02	7.04
Zn^2^+	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

Thiocyanate $\ce{SCN-}$	log $K_1$	log $K_2$	log $K_3$	log $K_4$	log $K_5$	log $K_6$
Mn^2^+	1.23
Fe^2^+	1.31
Co^2^+	1.71
Ni^2^+	1.76
Cu^2^+	2.33
Fe^3^+	3.02
Ag^+	4.8	3.43	1.27	0.2
Zn^2^+	1.33	0.58	0.09	–0.4
Cd^2^+	1.89	0.89	0.02	–0.5
Hg^2^+		17.26 ($\beta_2$)	2.71	1.83