| Popis: |
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. |
