Metal-ion interactions with sugars. Crystal structure and FT-IR study of PrCl3-d-ribose complex

A single-crystal of PrCl3·d-ribose·5H2O was obtained from a methanol-water solution and its structure determined by X-ray crystallography. Two configurations of the complex, as a pair of isomers, were found in the single-crystal in a disordered state, which differs from that reported previously. The ligand of one of the complexes is α-d-ribopyranose in the 4C1 conformation, and the ligand of the other is β-d-ribopyranose in the 1C4 conformation. The α:β anomeric ratio is 54:46. Both ligands of the two isomers provide three hydroxyl groups in an axial-equatorial-axial orientation for coordination. The Pr3+ ion is nine-coordinated, with five Pr-O bonds from water molecules, three Pr-O bonds from the hydroxyl groups of the d-ribopyranose and one Pr-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 are shifted in the complex, compared to those in d-ribose, and the IR results are in accord with those obtained from the X-ray diffraction study.