Synthesis, characterization and structural elucidation of a new sodium β-cyclodextrin-based metal-organic framework and the sodium chloride β-cyclodextrin inclusion complex

Le résumé fourni par la source

• A new sodium β-cyclodextrin metal-organic framework ( Na-β-CD ) was synthesized via the vapor diffusion method, in which NaH was initially explored as a source of sodium cations. • Recrystallization of Na-β-CD in an aqueous NaCl solution led to the formation of single crystals of the respective inclusion complex ( NaCl-β-CD ). • Single-crystal XRD of NaCl-β-CD revealed the formation of a host-guest inclusion complex of the hydrated Cl - ions within the bowl-like internal cavities of a sodium(I)-β-CD double chain polymer. In this work, a new sodium-based metal-organic framework with the oligosaccharide β-cyclodextrin ( Na-βCD ) was synthesized and characterized using a set of experimental techniques, and the sodium chloride β-cyclodextrin inclusion complex ( NaCl-β-CD ) was also prepared and its crystal structure elucidated. Na-β-CD was achieved via tetrahydrofuran vapor diffusion in a dimethylformamide solution of β-CD using for the first time sodium hydride (NaH) as a base in 1:1 molar ratio of NaH/β-CD. Subsequently, NaCl-β-CD was obtained by recrystallization of the prepared Na-β-CD in an aqueous solution of NaCl (1:1 molar ratio). SEM-EDX analysis showed the characteristic Na peaks for both compounds (1:1 Na/β-CD molar ratio) together with the Cl peaks only for NaCl-βCD (1:1 Cl/β-CD molar ratio), while ¹H NMR and FTIR spectra indicated that both compounds retain the β-CD skeleton, with minor modifications attributed to β-CD deprotonation in Na-β-CD and sodium coordination in both compounds. In fact, NaCl-β-CD exhibits a P 2 1 space group and its crystal structure reveals the formation of a sodium(I)-β-cyclodextrin double chain coordination polymer, whereas the hydrated Cl - ions are encapsulated within the bowl-like internal cavities of β-CD through hydrogen bonding interactions forming a host-guest (H 2 O) n Cl⊂β-CD inclusion complex. Consequently, this result demonstrates the ability of Na-βCD to incorporate chloride ions from aqueous solutions, and it paves the way for further research to extend the scope of β-CD-MOF-based materials.

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