Abstract
Chiral molecules preferentially form one-handed supramolecular assemblies that reflect the absolute configuration of the molecules. Under specific conditions, however, the opposite-handed supramolecular assemblies are also obtained because of flexibility in the bond length and reversibility of non-covalent interactions. The mechanism of the handedness selectivity or switching phenomenon remains ambiguous, and most phenomena are observed by chance. Here we demonstrate the construction of chiral hydrogen-bonded twofold helical assemblies with controlled handedness in the crystalline state based on crystallographic studies. Detailed investigation of the obtained crystal structures enabled us to clarify the mechanism, and the handedness of the supramolecular chirality was successfully controlled by exploiting achiral factors. This study clearly reveals a connection between molecular chirality and supramolecular chirality in the crystalline state.
Highlights
Chiral molecules preferentially form one-handed supramolecular assemblies that reflect the absolute configuration of the molecules
In conclusion, this study demonstrates the handedness switching of supramolecular chirality (SMC) of 1D ladder-type HB networks based on the twist of carboxylate groups with o-substituents on the achiral carboxylic acids due to steric repulsion
To the best of our knowledge, this is the first demonstration of handedness switching of SMC by achiral counter ions, and we have confirmed the switching based on crystal structures as well as vibrational circular dichroism (VCD) spectra
Summary
Chiral molecules preferentially form one-handed supramolecular assemblies that reflect the absolute configuration of the molecules. The study of chirality linkages between molecules and the crystalline helical assemblies at the supramolecular level remains challenging. Helical hydrogen-bonding (HB) networks have become a target in the elucidation of the linkage between MC and SMC (Fig. 1d); organic molecules with (R)- or (S)-configurations produce two enantiomers and four diastereomers to form supP or supM helical HB networks. The discrimination method was further applied to the 21-helices of HB networks of ammonium carboxylates[18] and Cinchona alkaloid derivatives[19], as well as other 21-helices[20,21,22] We focus on the control of their diastereomers with achiral components and present a plausible mechanism for the inversion of the SMC of HB helices
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