Cavity effect on perrhenate recognition by polyammonium cages

Valeria Amendola, Giancarla Alberti, Greta Bergamaschi, Raffaela Biesuz, Massimo Boiocchi, Stefania Ferrito, Franz Peter Schmidtchen

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40 Scopus citations


The affinity of azacryptands towards perrhenate has been investigated by potentiometric, 1H NMR spectroscopic and ITC studies in aqueous solutions. The association constants could only be determined for the p-xylyl and m-xylyl azacryptands in the hexaprotonated form. The experimental results showed the outstanding affinity of the p-xylyl cryptand for perrhenate, attributable to the geometric complementarity between the anion and the cavity of the receptor. Single crystals of the inclusion complex could also be obtained. The X-ray diffraction studies indicate that the perrhenate anion is included in the cavity of the receptor and interacts with the ammonium groups by means of both direct and water-mediated H-bonding interactions. The receptors were also investigated in the presence of different anions (i.e. chloride, bromide, iodide, perchlorate and nitrate). The affinity trend demonstrates that the p-xylyl cryptand cavity is more suitable to host large anionic guests such as perrhenate, perchlorate and iodide, despite their low density charge. On the contrary, nitrate, bromide and chloride fit better into the smaller cavity of the m-xylyl cryptand. The higher affinity of the m-xylyl cage towards chloride over that of perrhenate was also demonstrated by the crystal structure of the 1:1 adduct. The outstanding affinity of receptor 1H66+ towards ReO4-, in an acidic water solution, opens new perspectives for the development of selective materials for the extraction and recovery of the perrhenate anion for clinical and environmental purposes. The formation of an inclusion complex, [1H6(ReO4)](CF 3SO3)5, is confirmed by X-ray diffraction studies.

Original languageEnglish
Pages (from-to)3410-3417
Number of pages8
JournalEuropean Journal of Inorganic Chemistry
Issue number21
StatePublished - Jul 2012


  • Cryptands
  • Hydrogen bonds
  • Perrhenate anion
  • Receptors
  • Structure-energy correlations


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