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

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Abstract
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.
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