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.