INTERACTION OF ALKALINE-EARTH METAL-IONS WITH CARBOXYLIC-ACIDS IN AQUEOUS-SOLUTIONS STUDIED BY C-13 NMR-SPECTROSCOPY

C-13 NMR spectroscopic measurements of aqueous solutions containing al kaline earth metal chloride and a carboxylic acid have been carried ou t to acquire some insight into the coordination manners of various car boxylic acids to alkaline earth metal ions. The dependence of the C-13 NMR signal positions of the carboxylate carbons on the magnesium ion concentration in a magnesium carboxylate system is a good index to und erstand the coordination manner of the carboxylate ion. The upfield sh ift of the carboxylate carbon signal with increasing magnesium ion con centration indicates that the carboxylate ion acts as a bidentate liga nd to form a ring structure. Only in the citrate systems, the existenc e of a relatively stable complex is evidenced in which the citrate ion is expected to act as a tridentate ligand.