Skip to main content
Chemistry LibreTexts

16.12: Formation Constants

  • Page ID
    220809
  • 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 \(K_6\)
    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 \(K_4\) log \(K_5\) log \(K_6\)
    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 \(K_5\) 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 \(K_3\) log \(K_4\) log \(K_5\) log \(K_6\)
    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

    EDTA.png

    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

    Hydroxide

    \(\ce{OH-}\)

    log \(K_1\) log \(K_2\) log \(K_3\) log \(K_4\) log \(K_5\) log \(K_6\)
    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 \(K_4\) 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

    nitriloacetic.png

    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 \(K_3\) log \(K_4\) log \(K_5\) log \(K_6\)
    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

    phenanthroline.png

    log \(K_1\) log \(K_2\) log \(K_3\) log \(K_4\) log \(K_5\) log \(K_6\)
    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

    Thiocyanate

    \(\ce{SCN-}\)

    log \(K_1\) log \(K_2\) log \(K_3\) log \(K_4\) log \(K_5\) log \(K_6\)
    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

    • Was this article helpful?