Structure characterization of the non-crystalline complexes of copper salts with native cyclodextrins

Abstract

The characterization of non-crystalline complexes is particularly difficult when techniques like X-ray diffraction or NMR cannot be used. We propose a simple procedure to characterize the physicochemical properties of amorphous new coordination compounds between cyclodextrins (CD) and Cu²⁺ salts, by means of the integration of the information provided by several techniques including elemental analysis, flame atomic absorption, TGA, UV-Vis diffuse reflectance, colorimetry, FT-IR and EPR. On the basis of these procedures, we suggest geometrical and structural approximations resulting in an octahedral or distorted octahedral geometry with diverse positions for the metallic centre. According to the EPR spectrum, only one of the complexes may have rhombic symmetry. We also analyzed enthalpy–entropy compensation and the isokinetic effect. In addition, general trends in thermal stability, spectroscopic properties and inclusion in the cavity were analysed. This complete characterization methodology becomes essential for their future application as catalysts.