# 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 - -