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 |
