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Crystals 2018, 8(12), 457; https://doi.org/10.3390/cryst8120457 (registering DOI)

Cyclodextrin-Driven Formation of Double Six-Ring (D6R) Silicate Cage: NMR Spectroscopic Characterization from Solution to Crystals

1
Institut Lavoisier de Versailles, Centre National de la Recherche Scientifique, Université de Versailles St-Quentin, Université Paris-Saclay, 45 av. des Etats-Unis, 78035 Versailles CEDEX, France
2
Centre National de la Recherche Scientifique, Conditions Extrêmes et Matériaux: Haute Température et Irradiation, Université d’Orléans, 45071 Orléans, France
*
Author to whom correspondence should be addressed.
Received: 21 November 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
(This article belongs to the Special Issue NMR Crystallography)
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Abstract

Identification and isolation of secondary building units (SBUs) from synthesis media of zeolites still represent a challenging task for chemists. The cage structure anion Si12O3012− known as the double six-ring (D6R) was synthesized from α-cyclodextrin (α-CD) mediated alkaline silicate solutions and conditions of its stability and reactivity in aqueous solution were studied by using nuclear magnetic resonance (NMR) spectroscopy. A single crystal X-ray diffraction (XRD) analysis revealed a novel polymorph of the hybrid complex K12Si12O30·2α-CD·nD2O (n ≈ 30–40), which crystallizes in the orthorhombic C2221 space group symmetry with a = 14.841(4) Å, b = 25.855(6) Å, and c = 41.91(1) Å. The supramolecular adduct of the silicate anion sandwiched by two α-CDs forms a perfect symmetry matching the H-bonding donor-acceptor system between the organic macrocycle and the D6R unit. The driving force of such a hybrid assembly has found to be strongly dependent on the nature of the cation present as large alkali counter ions (K+, Rb+ and Cs+), which stabilize the D6R structure acting as templates. Lastly, we provided the first 29Si MAS NMR measurement of 3Q Si in an isolated D6R unit that allows the verification of the linear correlation between the chemical shift and <SiOSi> bond angle for 3Q Si species in DnR cages (n = 3, 4, 6).
Keywords: crystallization; nuclear magnetic resonance spectroscopy; hydrogen-bonding; silicate oligomers; self-assembly; molecular recognition; template effect crystallization; nuclear magnetic resonance spectroscopy; hydrogen-bonding; silicate oligomers; self-assembly; molecular recognition; template effect
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Haouas, M.; Falaise, C.; Martineau-Corcos, C.; Cadot, E. Cyclodextrin-Driven Formation of Double Six-Ring (D6R) Silicate Cage: NMR Spectroscopic Characterization from Solution to Crystals. Crystals 2018, 8, 457.

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