Sugar interaction with metal ions. The coordination behavior of neutral galactitol to Ca(II) and lanthanide ions

Abstract

The crystal structures of CaCl 2·galactitol·4 H 2O and 2EuCl 3·galactitol·14 H 2O were determined to compare the coordination behavior of Ca and lanthanide ions. The crystal system of the Ca–galactitol complex, CaCl 2·C 6H 14O 6·4 H 2O, is monoclinic, Cc space group. Each Ca ion is coordinated to eight oxygen atoms, four from two galactitol molecules and four from water molecules. Galactitol provides O-2, -3 to coordinate to one Ca 2+, and O-4, -5 with another Ca 2+, to form a chain structure. The crystal system of the Eu–galactitol complex, 2EuCl 3·C 6H 14O 6·14 H 2O, is triclinic, P1̄ space group. Each Eu ion is coordinated to nine oxygen atoms, three from an alditol molecule and six from water molecules. Each galactitol provides O-1, -2, -3 to coordinate with one Eu 3+ and O-4, -5, -6 with another Eu 3+. The other water molecules are hydrogen-bonded in the structure. The similar IR spectra of Pr–, Nd–, Sm–, Eu–, Dy–, and Er–galactitol complexes show that those lanthanide ions have the same coordination mode to neutral galactitol. The Raman spectra also confirm the formation of metal ion–carbohydrate complexes.