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Download fileAssembly of Chiral Cluster-Based Metal–Organic Frameworks and the Chirality Memory Effect during their Disassembly
journal contribution
posted on 2021-06-28, 21:29 authored by Guocheng Deng, Boon K. Teo, Nanfeng ZhengMany metal clusters are intrinsically
chiral but are often synthesized
as a racemic mixture. By taking chiral Ag14(SPh(CF3)2)12(PPh3)4(DMF)4 (Ag14) clusters with
bulky thiolate ligands as an example, we demonstrate herein an interesting
assembly disassembly (ASDS) strategy to obtain the corresponding,
optically pure crystals of both homochiral enantiomers, R-Ag14m and S-Ag14m. The ASDS strategy makes use of two bidentate linkers with
different chiral configurations, namely, (1R,2R,N1E,N2E)-N1,N2-bis(pyridin-3-ylmethylene)cyclohexane-1,2-diamine
(LR) and the corresponding chiral analogue LS. For comparison, we also use the racemic mixture of equimolar of LR and LS (LRS). Three three-dimensional
(3D) Ag14-based metal–organic frameworks (MOFs)
were characterized by X-ray crystallography to be [Ag14(SPh(CF3)2)12(PPh3)4(LR)2]n (Ag14-LR), [Ag14(SPh(CF3)2)12(PPh3)4(LS)2]n (Ag14-LS), and [Ag14(SPh(CF3)2)12(PPh3)4(LRS)2]n (Ag14-LRS), respectively. As expected, the
building blocks in Ag14-LR or Ag14-LS are homochiral R-Ag14 or S-Ag14, respectively. In contrast, Ag14-LRS is achiral and
crystallizes with a diamond-like structure containing alternate R-Ag14 and S-Ag14 clusters. During the assembly process, the racemic Ag14 clusters were converted to homochiral
building blocks, namely, R-Ag14 for Ag14-LR and S-Ag14 for Ag14-LS. Subsequently, the chiral linkers
were removed from the crystals of Ag14-LR and Ag14-LS via hydrolysis with water, and from the disassembled
solid material Ag14-DR and Ag14-DS, optically
pure enantiomers R-Ag14m and S-Ag14m were obtained. It is hoped
that this simple assembly strategy can be used to construct cluster-based
chiral assemblage materials and that the subsequent disassembly protocol
can be used to obtain optically pure chiral cluster molecules from
as-prepared racemic mixtures.
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Chirality Memory Effectchiral analogue LSPPh 3LRDMFN 1 Ehomochiral R-Ag 14chiral cluster moleculesas-prepared racemic mixturesR-Ag 14S-Ag 14homochiral building blocksASDSAg 14S-Ag 14 mLRSMOFchiral Ag 14R-Ag 14 mracemic mixtureenantiomers R-Ag 14 mDRDSracemic Ag 14 clustersS-Ag 14 clusterscluster-based chiral assemblage mat...material Ag 14