Preparation and spectroscopic characterization of two HoCl3–galactitol complexes and one ErCl3–galactitol complex

The interactions between metal ions and hydroxyl groups of carbohydrates are important for their possible biological activities. Here two HoCl3–galactitol complexes ([Ho(galac)(H2O)3)]Cl3·0.5galac) (HoG(I)) and ([Ho2(galac)(H2O)12)]Cl6·2H2O) (HoG(II))) and one ErCl3–galactitol complex ([Er(galac)(H2O)3)]Cl3·0.5galac)(ErG)) were prepared and characterized. The possible structures of HoG(I) and ErG were deduced from FTIR, elemental analysis, ESI-MS, FIR, THz and TGA results. It is suggested that Ho3+ or Er3+ is 9-coordinated with six hydroxyl groups from two galactitol molecules and three water molecules, and another galactitol molecule is hydrogen-bonded in HoG(I) and ErG and the ratio of metal to ligand is 1:1.5. The structure of HoG(II) was determined by FTIR and X-ray diffraction analyses. The results demonstrate that lanthanide ions with galactitol may form two compounds in a system and different topological structures can be obtained.