A general coordination‐ionization scheme for polyhydroxy carboxylic acids in water

Abstract

Abstract The structural changes of coordination compounds of polyhydroxy carboxylic acids as a function of the pH are discussed. A general coordination‐ionization scheme, based on literature data and covering some forty cations, is provided. The following trend is observed on going from low to high pH: ( i )bidentate coordination of the cation by the α‐hydroxy carboxylic acid moiety, ( ii ) ionization of the carboxylic acid function, ( iii ) ionization of the α‐hydroxyl group and ( iv ) coordination by an ionized‐diol function. For complexes of metal ions, the pH effects are correlated with the acidity of the hydrated cation and explained using an extended electrostatic model. The coordination‐ionization scheme provides an explanation for and allows prediction of both metal‐ion‐catalyzed addition reactions and synergetic effects in sequestering agents.