Skip to main content
Chemistry LibreTexts

E4a: Stepwise Association Constants

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 \(CH_3COO^{-}\) 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: 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: 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: 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
A12ethylenediamine.jpg

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
A12edta.jpg

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: 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: 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: 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
A12nitriloacetate.jpg
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: 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

A121,10-phenanthroline.jpg

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: S2O32– log K1 log K2 log K3 log K4 log K5 log K6
Ag+ (T = 20 oC) 8.82 4.85 0.53      
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