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E4: Complex Ion Formation Constants

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    A stability constant is an equilibrium constant for the formation of a complex in solution that measures the strength of the interaction between the ligands and metal that form the complex. The formation of complexes between a metal ion, M, and ligands, L, is really a ligand exchange (i.e., substitution reaction) with metal ions in aqueous solutions present as aqua-ligated ions.

    Halo Ligands \(K_f\)
    Al3+ + 6 F- \(\rightleftharpoons\) [AlF6]3- 2.5 x 104
    Al3+ + 4 F- \(\rightleftharpoons\) [AlF4]-1 2.0 x 108
    Be2+ + 4 F- \(\rightleftharpoons\) [BeF4]2- 1.3 x 1013
    Sn4+ + 6 F- \(\rightleftharpoons\) [SnF6]2- 1.0 x 1025
    Cu+ + 2 Cl- \(\rightleftharpoons\) [CuCl2]-1 3.0 x 105
    Ag+ + 2 Cl- \(\rightleftharpoons\) [AgCl2]-1 1.8 x 105
    Pb2+ + 4 Cl- \(\rightleftharpoons\) [PbCl4]2- 2.5 x 1015
    Zn2+ + 4 Cl- \(\rightleftharpoons\) [ZnCl4]2- 1.6
    Hg2+ + 4 Cl- \(\rightleftharpoons\) [HgCl4]2- 5.0 x 1015
    Cu+ + 2 Br- \(\rightleftharpoons\) [CuBr2]-1 8.0 x 105
    Ag+ + 2 Br- \(\rightleftharpoons\) [AgBr2]-1 1.0 x 1011
    Hg2+ + 4 Br- \(\rightleftharpoons\) [HgBr4]2- 3.0 x 104
    Cu+ + 2 I- \(\rightleftharpoons\) [CuI2]-1 8.0 x 108
    Ag+ + 2 I- \(\rightleftharpoons\) [AgI2]-1 1.0 x 1011
    Pb2+ + 4 I- \(\rightleftharpoons\) [PbI4]2- 3.0 x 104
    Hg2+ + 4 I- \(\rightleftharpoons\) [HgI4]2- 1.9 x 1030
    Ammine Ligands \(K_f\)
    Ag+ + 2 NH3 \(\rightleftharpoons\) [Ag(NH3)2]+ 1.6 x 107
    Zn2+ + 4 NH3 \(\rightleftharpoons\) [Zn(NH3)4]2+ 7.8 x 108
    Cu2+ + 4 NH3 \(\rightleftharpoons\) [Cu(NH3)4]2+ 1.1 x 1013
    Hg2+ + 4 NH3 \(\rightleftharpoons\) [Hg(NH3)4]2+ 1.8 x 1019
    Co2+ + 6 NH3 \(\rightleftharpoons\) [Co(NH3)6]2+ 5.0 x 104
    Co3+ + 6 NH3 \(\rightleftharpoons\) [Co(NH3)6]3+ 4.6 x 1033
    Cd2+ + 6 NH3 \(\rightleftharpoons\) [Cd(NH3)6]2+ 2.6 x 105
    Ni2+ + 6 NH3 \(\rightleftharpoons\) [Ni(NH3)6]2+ 2.0 x 108
    Cyanide Ligands \(K_f\)
    Fe2+ + 6 CN- \(\rightleftharpoons\) [Fe(CN)6]4- 1.0 x 1024
    Fe3+ + 6 CN- \(\rightleftharpoons\) [Fe(CN)6]3- 1.0 x 1031
    Ag+ + 2 CN- \(\rightleftharpoons\) [Ag(CN)2]-1 5.3 x 1018
    Cu+ + 2 CN- \(\rightleftharpoons\) [Cu(CN)2]-1 1.0 x 1016
    Cd2+ + 4 CN- \(\rightleftharpoons\) [Cd(CN)4]2- 7.7 x 1016
    Au+ + 2 CN- \(\rightleftharpoons\) [Au(CN)2]-1 2.0 x 1038
    Other monodentate ligands \(K_f\)
    Ag+ + 2 CH3NH2 \(\rightleftharpoons\) [Ag(CH3NH2)2]+1 7.8 x 106
    Cd2+ + 4 SCN- \(\rightleftharpoons\) [Cd(SCN)4]2- 1.0 x 103
    Cu2+ 2 SCN- \(\rightleftharpoons\) [Cu(SCN)2] 5.6 x 103
    Fe3+ 3 SCN- \(\rightleftharpoons\) [Fe(SCN)3] 2.0 x 106
    Hg2+ 4 SCN- \(\rightleftharpoons\) [Hg(SCN)4]2- 5.0 x 1021
    Cu2+ 4 OH- \(\rightleftharpoons\) [Cu(OH)4]2- 1.3 x 1016
    Zn2+ 4 OH- \(\rightleftharpoons\) [Zn(OH)4]2- 2.0 x 1020
    Bidentate ligands \(K_f\)
    Mn2+ + 3 en \(\rightleftharpoons\) [Mn(en)3]2+ 6.5 x 105
    Fe2+ + 3 en \(\rightleftharpoons\) [Fe(en)3]2+ 5.2 x 109
    Co2+ + 3 en \(\rightleftharpoons\) [Co(en)3]2+ 1.3 x 1014
    Co3+ + 3 en \(\rightleftharpoons\) [Co(en)3]3+ 4.8 x 1048
    Ni2+ + 3 en \(\rightleftharpoons\) [Ni(en)3]2+ 4.1 x 1017
    Cu2+ + 2 en \(\rightleftharpoons\) [Cu(en)2]2+ 3.5 x 1019
    Co2+ + 3 C2O42- \(\rightleftharpoons\) [Co(C2O4)3]4- 4.5 x 106
    Fe3+ + 3 C2O42- \(\rightleftharpoons\) [Fe(C2O4)3]3- 3.3 x 1020

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    E4: Complex Ion Formation Constants is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.

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