Enhanced Surface Ligands Reactivity of Metal Clusters by Bulky Ligands for Controlling Optical and Chiral Properties

Abstract

Surface ligands play critical roles in determining the surface properties of metal clusters.H owever,m odulating the properties and controlling the surface structure of clusters through surface-capping-agent displacement is challenging. Herein, [Ag 14 (SPh(CF 3 ) 2 ) 12 (PPh 3 ) 4 (DMF) 4 ]( Ag 14 -DMF; DMF = N,N-dimethylformamide), with weakly coordinated DMF ligands on surface silver sites,w as synthesized by am ixed-ligands strategy.O wing to the high surface reactivity of Ag 14 -DMF,the surface ligands are labile,easily dissociated or exchanged by other ligands.Based on the enhanced surface reactivity,easy modulation of the optical properties of Ag 14 by reversible "on-off" DMF ligation was realized. When chiral amines were introduced to as-prepared products,a ll eight surface ligands were replaced by amines and the racemic Ag 14 clusters were converted to optically pure homochiral Ag 14 clusters as evidenced by circular dichroism (CD) activity and single-crystal X-raydiffraction (SCXRD). This work provides anew insight into modulation of the optical properties of metal clusters and atomically precise homochiral clusters for specific applications are obtained.

Assembly of Chiral Cluster-Based Metal–Organic Frameworks and the Chirality Memory Effect during their Disassembly

“…Ag 14 (SPh-(CF 3 ) 2 ) 12 (PPh 3 ) 4 (DMF) 4 was prepared via a literature reported method. 40 AgNO 3 (50.0 mg) and 50 mg of PPh 3 were dissolved in a mixture solution of N,N-dimethylformamide and dichloromethane. Then, 40 μL of 3,5-bis(trifluoromethyl)benzenethiol was added.…”

“…Furthermore, the as-prepared racemate clusters can be converted to optically pure enantiomers through post-treatment with small chiral molecules such as R-or S-1-phenylpropylamine (which replaces all surface PPh 3 and DMF ligands). 40 The high flexibility of the ligand shell of the Ag 14 cluster as well as the existence of the weak coordination DMF ligands make it a good candidate as a building block for constructing CMOFs and investigating the relationship between the linkers and building units.…”

“…The Ag 14 cluster (Figure 2a) was prepared via the literature method. 40 The linkers LR and LS (Figure 2b,c) were synthesized via a dehydration condensation reaction of chiral (1R,2R)-(+)-1,2-diaminocyclohexane or (1S,2S)-(−)-1,2-diaminocyclohexane and 3-pyridinecarbaldehyde, respectively. 41 The 1 H NMR and 13 C NMR spectra of LS are shown in Figures S1 and S2, respectively.…”

“…As reported in a previous publication, the four Ag sites coordinated with DMF or other molecules in Ag 14 cluster possess high reactivities. 40 The molecules coordinated on it can easily dissociate or be replaced by other molecules. During the assembly process of Ag 14 -LR or Ag 14 -LS, the as-prepared racemic Ag 14 clusters were converted to homochiral R-Ag 14 or S-Ag 14 , respectively, by the chiral linkers.…”

Revealing the chirality origin and homochirality crystallization of Ag14 nanocluster at the molecular level

“…hirality is ubiquitous in (supra)molecular structures, such as DNA in living organisms and natural products in plants, which plays a pivotal role in biological activity, catalysis, medicines, and a variety of other applications 1,2 . Although the enantioselective preparation and separation of chiral small molecules induced by chiral reagents have been well established, the realization of this process with achiral reagents still faces great challenges, especially for these higher-order motifs such as nanoclusters, nanoparticles, and supramolecules [3][4][5][6][7][8][9][10][11][12][13][14] . Recent research on the origin of chirality formed in achiral systems has led to great advances in chiral metal nanoclusters protected by achiral ligands; the origin of chirality of them has been typically classified into three types: (1) chiral arrangement of inner metal core atoms; 15,16 (2) asymmetric arrangement of surface structure to form a chiral shell; [17][18][19][20][21] (3) distortion or rotation induced structure chirality [22][23][24] .…”