A thorough synthesis and structural investigation of a new generation of halide inclusion complexes of sodium β-cyclodextrin-based metal organic frameworks.

We report, for the first time, the ability of sodium(I)-based β-CD-MOFs (Na-β-CD-MOFs) to form Inclusion complexes (IC) with all the common halides, abbreviated as NaX-β-CD (X = F-, Cl-, Br- or I-). NaX-β-CD were obtained by a straightforward reaction of β-CD in an aqueous medium containing sodium halide (NaX) in an equimolar ratio, followed by the addition of a small amount of ethanol to induce crystallisation at room temperature. This series has been thoroughly characterised using single-crystal and powder XRD analysis, SEM-EDX, FTIR and 1H NMR spectroscopies. Morphological analysis via SEM revealed the coexistence of porous and block-shaped crystals, while EDX spectra confirmed the presence of sodium cations and the corresponding halide anions. Single-crystal X-ray diffraction analysis of NaF-β-CD shows the formation of a cationic sodium(I)-β-cyclodextrin double chain coordination polymer, whereas the F- anions are encapsulated within the bowl-like internal cavities of β-CD through a strong hydrogen bonding interaction, forming a host-guest (H2O)nF ⊂ β-CD IC. Powder XRD analysis of NaX-β-CD revealed that all these β-CD-MOF-based ICs are isostructural, regardless of the size of the halide anion (X = F-, Cl-, Br- or I-). FTIR and 1H NMR spectra confirmed the preservation of the β-CD skeleton, with minor changes in peak intensity and position.