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Asymmetric Synthesis of Chiral Bimetallic [Ag28Cu12(SR)24]4– Nanoclusters via Ion Pairing
- Yan, Juanzhu, Su, Haifeng, Yang, Huayan, Hu, Chengyi, Malola, Sami, Lin, Shuichao, Teo, Boon K., Häkkinen, Hannu, Zheng, Nanfeng
- Journal of the American Chemical Society 2016 v.138 no.39 pp. 12751-12754
- X-radiation, ammonium salts, cations, enantiomers, mass spectrometry, nanoparticles
- In this work, a facile ion-pairing strategy for asymmetric synthesis of optically active negatively charged chiral metal nanoparticles using chiral ammonium cations is demonstrated. A new thiolated chiral three-concentric-shell cluster, [Ag₂₈Cu₁₂(SR)₂₄]⁴–, was first synthesized as a racemic mixture and characterized by single-crystal X-ray structure determination. Mass spectrometric measurements revealed relatively strong ion-pairing interactions between the anionic nanocluster and ammonium cations. Inspired by this observation, the as-prepared racemic mixture was separated into enantiomers by employing chiral quaternary ammonium salts as chiral resolution agents. Subsequently, direct asymmetric synthesis of optically active enantiomers of [Ag₂₈Cu₁₂(SR)₂₄]⁴– was achieved by using appropriate chiral ammonium cations (such as N-benzylcinchoninium vs N-benzylcinchonidinium) in the cluster synthesis. These simple strategies, ion-pairing enantioseparation and direct asymmetric synthesis using chiral counterions, may be of general use in preparing chiral metal nanoparticles.