Stability constants of chelates and EDTA complexes

Stepwise formation constants of ethylenediamine complexes, the Co²⁺–NH₃ system, and the 1 : 1 formation constants of 13 metal ions with EDTA. The chelate-effect and conditional-EDTA calculations use this table; ammonia, halide and other monodentate systems are in the table of formation constants of complex ions.


$\ce{Cu^2+}$	ethylenediamine (en)	$\ce{[Cu(en)]^2+}$	1	10.48	10.48	25 °C, I = 0
$\ce{Cu^2+}$	ethylenediamine (en)	$\ce{[Cu(en)2]^2+}$	2	9.07	19.55	25 °C, I = 0
$\ce{Ni^2+}$	ethylenediamine (en)	$\ce{[Ni(en)]^2+}$	1	7.38	7.38	25 °C, I = 0
$\ce{Ni^2+}$	ethylenediamine (en)	$\ce{[Ni(en)2]^2+}$	2	6.18	13.56	25 °C, I = 0
$\ce{Ni^2+}$	ethylenediamine (en)	$\ce{[Ni(en)3]^2+}$	3	4.11	17.67	25 °C, I = 0
$\ce{Zn^2+}$	ethylenediamine (en)	$\ce{[Zn(en)]^2+}$	1	5.66	5.66	25 °C, I = 0
$\ce{Zn^2+}$	ethylenediamine (en)	$\ce{[Zn(en)2]^2+}$	2	4.98	10.64	25 °C, I = 0
$\ce{Zn^2+}$	ethylenediamine (en)	$\ce{[Zn(en)3]^2+}$	3	3.25	13.89	25 °C, I = 0
$\ce{Cd^2+}$	ethylenediamine (en)	$\ce{[Cd(en)]^2+}$	1	5.41	5.41	25 °C, I = 0
$\ce{Cd^2+}$	ethylenediamine (en)	$\ce{[Cd(en)2]^2+}$	2	4.50	9.91	25 °C, I = 0
$\ce{Cd^2+}$	ethylenediamine (en)	$\ce{[Cd(en)3]^2+}$	3	2.78	12.69	25 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)]^2+}$	1	1.99	1.99	20 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)2]^2+}$	2	1.51	3.50	20 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)3]^2+}$	3	0.93	4.43	20 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)4]^2+}$	4	0.64	5.07	20 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)5]^2+}$	5	0.06	5.13	20 °C, I = 0
$\ce{Co^2+}$	ammonia (NH₃)	$\ce{[Co(NH3)6]^2+}$	6	−0.73	4.40	20 °C, I = 0
$\ce{Ag+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[AgY]^3-}$	1	7.32	7.32	20 °C, I = 0.1 M
$\ce{Ba^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[BaY]^2-}$	1	7.86	7.86	20 °C, I = 0.1 M
$\ce{Mg^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[MgY]^2-}$	1	8.79	8.79	20 °C, I = 0.1 M
$\ce{Ca^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[CaY]^2-}$	1	10.69	10.69	20 °C, I = 0.1 M
$\ce{Al^3+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[AlY]-}$	1	16.30	16.30	20 °C, I = 0.1 M
$\ce{Co^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[CoY]^2-}$	1	16.31	16.31	20 °C, I = 0.1 M
$\ce{Cd^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[CdY]^2-}$	1	16.46	16.46	20 °C, I = 0.1 M
$\ce{Zn^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[ZnY]^2-}$	1	16.50	16.50	20 °C, I = 0.1 M
$\ce{Pb^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[PbY]^2-}$	1	18.04	18.04	20 °C, I = 0.1 M
$\ce{Ni^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[NiY]^2-}$	1	18.62	18.62	20 °C, I = 0.1 M
$\ce{Cu^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[CuY]^2-}$	1	18.80	18.80	20 °C, I = 0.1 M
$\ce{Hg^2+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[HgY]^2-}$	1	21.70	21.70	20 °C, I = 0.1 M
$\ce{Fe^3+}$	EDTA⁴⁻ (Y⁴⁻)	$\ce{[FeY]-}$	1	25.10	25.10	20 °C, I = 0.1 M

Ethylenediamine and ammonia data are for 25 °C and I = 0 (Co²⁺–NH₃ at 20 °C); EDTA data are for 20 °C and I = 0.1 M and refer to the fully deprotonated Y⁴⁻. For a titration, multiply by α(Y⁴⁻) to get the conditional constant: α(Y⁴⁻) = 0.30 at pH 10.

Sources

A. E. Martell, R. M. Smith, Critical Stability Constants, vols. 1–6, Plenum (1974–1989), as tabulated in D. Harvey, Analytical Chemistry 2.1, Appendix 12.
N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann (1997), p. 910 (the chelate effect).

Used in these lessons

Stability and the chelate effect