Interaction between metal nitrates and carbohydrates: the topology coordination behavior of galactitol with trivalent lanthanide and divalent alkaline earth ions

It has long been known that metal ions and saccharides are involved in many biochemical processes. In this paper, metal nitrates were used as reactants to detect the coordination structures of the hydroxyl groups of galactitol in different environments. Three novel crystal structures and FT-IR spectra of metal nitrate-galactitol complexes of La(NO3)3.C6H14O6.(4)H2O, 2Ca(NO3)2.C6H14O6.H2O, and Sr(NO3)2.C6H14O6 were examined in an effort to clarify the structural factors that control metal ion interactions with saccharides in aqueous and biological systems. The coordination structures of galactitol with alkaline earth and lanthanide nitrates in the solid state were compared using FT-IR, Raman, and X-ray diffraction techniques to extensively discuss the coordination rules of different kinds of metal ions. Results provided a model of the coordination sites found in sugars and showed that the introduction of NO3- made the coordination modes of galactitol more diverse and complex than those of the corresponding chloride complexes. Specifically, new coordination modes of galactitol and complicated topology networks were found in 2Ca(NO3)2.C6H14O6.H2O and Sr(NO3)2.C6H14O6. FT-IR results are consistent with the crystal structures and thus provide the possibility of using the similarity of IR spectra to speculate about unknown structures when the compounds are difficult to prepare as single crystals.