Abstract
D-fructose reacts with the calcium ion to give complexes of the type Ca(δ- d-fructose)Cl 2-2H 2O, Ca(⨿- D-fructose) 2 Cl 2·3H 2O and Ca(⨿- d-fructose)Br 2-2H 2O. The infrared spectra of the free⨿- d-fructose and its calcium compounds are examined and a correlation between the spectral changes and the coordination sites involved has been established. Structurally known Ca(⨿- d-fructose)Cl 2· 2H 2O and its isomorphous Ca(⨿- d-fructose)Br 2·2H 2O showed that each calcium ion is seven-coordinated, binding to three symmetry related fructose molecules through O(2), O(3) of the first, O(4), O(5) of the second, and O(1) of the third molecule as well as to two water molecules, whereas in the Ca(⨿- d-fructose) 2Cl 2 · 3H 2O compound the calcium cation is eight coordinated, binding to two sugar molecules via O(1), O(4), and O(5) of each sugar moiety, as well as to two water molecules. Spectroscopic evidence presented here indicated that the two structurally dissimilar 1:1 and 2:1 calcium chloride adducts are spectrally different, while the 1:1 calcium chloride and the bromide complexes have virtually identical infrared spectra. The rearrangement of the strong hydrogen bonding network of the free sugar occurred upon metalation. Furthermore, the band assignments in the OH stretching region have been correlated with the sugar intermolecular hydrogen-bonding O O distances reported from the x-ray and the neutron diffraction measurements.
Published Version
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