Prediction of Stability Constants for Cr(III) and Cr(II) Complexes

Regression analysis was used to derive equations for estimaing thermodynamic stability constants for complexes of Cr²⁺ (log^° ₁Cr²⁺L] = 0.53log^° _n H _n L]) and Cr³⁺ (log^° ₁Cr³⁺L] = 0.88log^° _n H _n L]) from the known protonation constants of H _n L ligands and for determining stability constants of Cr²⁺ and Cr³⁺ complexes from the available stability constants of Cu²⁺ complexes (log^° ₁Cr²⁺L] = 0.76log^° ₁Cu²⁺L] and log^° ₁Cr²⁺L] = 0.60log^° ₁Cr³⁺L], respectively). Parameters of the Panteleon–Ecka equation for calculating stability constants of Cr²⁺ complexes ( = 0.57) and Cr³⁺ complexes ( = 0.69) with two and three bidentate ligands were also determined. The ratio of logarithmic stability constants for complexes with the same metals but with different metal ionic charges was found to be approximately equal to the ratio of charges on the central ions. The stability constant of Cr(II) sulfate complex was calculated.