Diaquabis(diamine)chromium(III) complexes: Acid dissociation constants and isomerization

Abstract

Acid dissociation constants are reported for the following equilibria: trans-Cr(A)(B)(H2O)₂³⁺(aq) + H2O ↔ trans-Cr(A)(B)(OH)(H₂O)²⁺(aq)+H₃O⁺(aq) pK₁ trans-Cr(A)(B)(OH)(H₂O)²⁺(aq) + H₂O ↔ trans-Cr(A)(B)(OH)₂⁺(aq)+H₃O⁺(aq) pK₂ where A = B = en; A = B = tmd; A = en, B = tmd. Similar results were obtained for each complex: pK₁ c. 4.2, pK₂ c. 7.6; 1M NaNO₃, 25°. The results are compared with pK data for related complexes of chromium and cobalt. The complex Cr(en)₂(H₂O)(OH)²⁺ undergoes extensive Cr-N bond rupture to yield deaminated products.