Metal-ion interactions with sugars. Crystal structures and FT-IR studies of the LaCl3–ribopyranose and CeCl3–ribopyranose complexes Original Research Article

Single crystals of LaCl3·C5H10O5·5H2O (1) and CeCl3·C5H10O5·5H2O (2) were obtained from ethanol–water solutions and their structures determined by X-ray. The two complexes are isomorphous. Two configurations of complex 1 or complex 2, as a pair of isomers, were found in each single crystal in a disordered state. The ligand of one of the isomer is α-d-ribopyranose in the 4C1 conformation, the ligand of the other is β-d-ribopyranose in the 1C4 conformation. For complex 1, the α:β anomeric ratio is 51:49, and for complex 2, the ratio is 52:48. Both ligands of the two isomers provide three hydroxyl groups in ax–eq–ax orientation for coordination. The Ln3+ (Ln = La or Ce) ion is nine-coordinated with five Ln–O bonds from water molecules, three Ln–O bonds from hydroxyl groups of the d-ribopyranose, and one Ln–Cl bond from chloride ion. The hydroxyl groups, water molecules, and chloride ions form an extensive hydrogen-bond network. The IR spectral C–C, O–H, C–O, and C–O–H vibrations were observed to be shifted in both the two complexes and the IR results are in accord with those of X-ray diffraction.