Formation Constants of Chromium(II) Complexes with (O,O)-, (O,N)- and (N,N)-Type Ligands and Comparison with Those of the Other First Transition Metal Complexes

The formation constants of the bivalent chromium complexes with various chelating ligands were determined by the pH titration method at the ionic strength μ=0.1 and at 25°C. The values of the formation constants for (O,O)-type complexes were logk1=3.85±0.05 and logk2=2.96±0.05 for oxalate ion, logk1=3.92±0.05 and logk2=3.21±0.05 for malonate ion, and logk1=9.89±0.05 for sulfosalicylate ion: for (O,N)-type complexes we obtained logk1=7.72±0.05 and logk2=7.54±0.05 for glycine, logk1=9.05±0.05 for 8-hydroxyquinoline, and logk1=7.53±0.05 for β-alanine. Based on these values together with the corresponding values of the (N,N)-type complexes, the effect of the coordinating atoms and of the number of members in a chelate ring upon the stabilities was discussed. These values were compared with those for the other transition metal complexes.