The formation constants of chromium(III) complexes with the oxalate ion, which is the simplest bidentate ligand coordinating by two oxygen atoms, have been determined by the pH method. It has been shown that the formation constants of oxalato chromium(III) complexes are larger than those of the corresponding titanium-(III) complexes, but smaller than those of the corresponding manganese(III), iron(III) and cobalt(III) complexes in the first transition series. The formation constants of oxalato chromium(III) complexes have been found to be remarkably smaller than those of the ethylenediamine chromium(III) complexes. This result suggests that two nitrogen atoms form a more stable complex with chromium than do the two oxygen atoms serving as donors in the bidentate chelate.

1) By measuring the conductivity of the solution of hexa-aquochromium(III) sulfate and potassium-chrome alum, the formation constant of the ion-pair [Cr(H2O)6]SO4+ has been calculated. 2) By measuring the pH, ion exchange separation and electrical conductivity of the heated solution of potassium-chrome alum and of the solution of the alum heated in the solid state, their ion compositions have been deduced. Appreciation is expressed to Messrs. Teruyoshi Fujishima and Tosuke Imamura for their help in the determination of the electrical conductivity.