Symmetry breaking of highly symmetrical nanoclusters for triggering highly optical activity

Developing new approaches to fulfill the enantioseparation of nanocluster racemates and construct cluster-based nanomaterials with optical activity remains highly desired in cluster science, because it is an essential prerequisite for fundamental research and extensive applications of these nanomaterials. We herein propose a strategy termed “active-site exposing and partly re-protecting” to trigger the symmetry breaking of highly symmetrical nanoclusters and to render cluster crystals optically active. The vertex PPh3 of the symmetrical Ag29(SSR)12(PPh3)4 (SSR = 1, 3-benzenedithiol) nanocluster was firstly dissociated in the presence of counterions with large steric hindrance, and then the exposed Ag active sites of the obtained Ag29(SSR)12 nanocluster were partly re-protected by Ag+, yielding an Ag29(SSR)12-Ag2 nanocluster with a symmetry-breaking construction. Ag29(SSR)12-Ag2 followed a chiral crystallization mode, and its crystal displayed strong optical activity, derived from CD and CPL characterizations. Overall, this work presents a new approach (i.e., active-site exposing and partly re-protecting) for the symmetry breaking of highly symmetrical nanoclusters, the enantioseparation of nanocluster racemates, and the achievement of highly optical activity.


Introduction
Chirality has long been one of the most important research topics since it is an amazing phenomenon ubiquitous in life, nature, and the universe ranging from nanoscale molecules (e.g., proteins, sugars, and DNA) to mater-scale substances (e.g., eyes, shells, and flowers), and to the vast galaxy [1][2][3] .As one of the most appealing characteristics of nanostructures, optical activity, including circular dichroism (CD), circular polarized luminescence (CPL), and vibrational circular dichroism (VCD), has attracted much attention and been considered as the prerequisite to exploit chirality-related applications [ 4 , 5 ].The study of chirality dated back to 1811 when the optical activity was observed in asymmetric quartz crystal by François Arago, after which tremendously experimental and theoretical efforts were made [6][7][8] .In nanoscience, the optical activity is generally achieved either by constructing metal nanoparticle-based assemblies in chiral arrangements or by the conjugation of metal nanoparticles with peripheral chiral molecules [9][10][11] .Indeed, the large-sized nanoparticle itself without chiral stabilizers is almost optically inactive in light of its homogeneous and symmetrical packing in the metallic kernel.In vivid contrast, metal nanoclusters, routinely described as ultrasmall metal nanoparticles [12][13][14][15][16][17][18][19][20][21][22][23] , have been exploited as ideal platforms to investigate the intrinsic chirality of metal-lic kernels, owing to their plentiful kernel constructions and kernelsurface bonding environments [24][25][26] .
The chirality of nanoclusters mainly originates from three aspects: (i) chirality in the metallic kernel, (ii) chirality in the metal-ligand interface, and (iii) chirality in the peripheral carbon group [27][28][29][30][31][32][33][34][35][36][37][38] .Among these aspects, the first aspect (i.e., chiral metallic kernel) has attracted much scientific interest since it not only represents the most intrinsic character in analyzing the origin of chirality in nanomaterials, but also exists in the other two aspects due to the transmission effect via intracluster interactions [39] .Besides, aside from nanoclusters with chiral peripheral ligands, most structurally asymmetrical nanoclusters with achiral ligands are racemic in their solutions and crystals [ 40 , 41 ].In this context, the chiral separation of these racemic clusters is an essential prerequisite for their fundamental research and extensive applications.Although several approaches (e.g., high-performance liquid chromatography separation and chiral self-assembly) have been exploited to separate cluster enantiomers from their racemates [42][43][44][45][46][47] , the enantioseparation has only been accomplished in limited examples.New approaches to fulfill the chiral resolution of nanocluster racemates and construct cluster-based nanomaterials with optical activity remain highly desired in cluster science.
Herein, a strategy termed "active-site exposing and partly reprotecting " was proposed to trigger the symmetry breaking of highly https://doi.org/10.1016/j.fmre.The DTAB addition-induced PPh 3 dissociation rendered vertex active Ag of the Ag 29 -PPh 3 nanocluster exploring, while the obtained Ag 29 cluster still adhered to the racemic crystallization.Besides, the Ag + addition triggered the re-protection of partly exposed Ag active sites and the symmetry breaking of the nanocluster, and the crystallization of Ag 29 -Ag cluster entities follows a chiral mode.

Nanocluster transformation from Ag 29 -PPh 3 to Ag 29 (SSR) 12 (Ag 29 )
30 mg of the Ag 29 -PPh 3 crystal was dissolved in 10 mL of DMF, and 50 mg of DTAB was added under vigorous stirring.After 30 min, the organic layer was separated to produce the Ag 29 nanocluster, which was used for crystallization directly.The yield was 95% based on the Ag element (calculated from the Ag 29 -PPh 3 ).

Crystallization of the Ag 29 nanocluster series
Single crystals of these Ag 29 nanoclusters were cultivated at 15 °C by vapor diffusing the ethyl ether into a DMF solution of the cluster.After 2 weeks, red crystals were collected, and the structures of these Ag 29 nanoclusters were determined.

Preparation of nanocluster crystalline films
The concentration of the DMF/CH 2 Cl 2 (1:9 of the volume ratio) solution of these Ag 29 nanoclusters was set as 30 mg/mL and then the solution was filtered with a 0.2 μm syringe filter.The solutions were stored for 12 h before use.50 μL of the solutions were dropped onto a quartz substrate, and spin-coated (using LAURELL WS-650MZ-23NPPB) at 1000 rpm for 60 s.The cluster-impregnated quartz substrate was dried in the air for 12 h before the optical property characterization.

Characterizations
The optical absorption spectra of nanoclusters were recorded using an Agilent 8453 diode array spectrometer.
The photoluminescence (PL) spectra were measured on a FL-4500 spectrofluorometer with the same optical density.
Electrospray ionization mass spectrometry (ESI-MS) measurements were performed by a Waters XEVO G2-XS QTof mass spectrometer.The sample was directly infused into the chamber at 5 L/min.For preparing the ESI samples, nanoclusters were dissolved in DMF (1 mg/mL) and diluted ( v / v = 1:1) by CH 3 OH. 31P nuclear magnetic resonance (NMR) spectra were acquired using a Bruker 600 Avance III spectrometer equipped with a Bruker BBO multinuclear probe (BrukerBioSpin, Rheinstetten, Germany).
The circularly polarized luminescence (CPL) spectra of nanoclusters were recorded using a JASCO CPL-300 instrument.For CPL measurements, the parameters were set as follows: scanning speed of 200 nm/min, response time of 2 s, band width of 10 nm, accumulations of 6.
The circular dichroism (CD) spectra were measured on a JASCO J-1500 circular dichroism spectrophotometer.The solid samples were measured with a DRCD-574 solid samples accessories, using an integrating sphere to detect the diffuse reflectance of samples.

X-Ray crystallography
The data collection for single-crystal X-ray diffraction (SC-XRD) of all nanocluster crystal samples was carried out on Stoe Stadivari diffractometer under nitrogen flow, using graphite-monochromatized Cu K  radiation (  = 1.54186Å).Data reductions and absorption corrections were performed using the SAINT and SADABS programs, respectively.The structure was solved by direct methods and refined with full-matrix least squares on F 2 using the SHELXTL software package.All non-hydrogen atoms were refined anisotropically, and all the hydrogen atoms were set in geometrically calculated positions and refined isotropically using a riding model.

Results and discussion
The Ag 29 -PPh 3 nanocluster was prepared using the previously reported procedure [48] .The introduction of DTAB (N,N,N-trimethyl-1dodecanaminium bromide) induced the transformation from Ag 29 -PPh 3 to Ag 29 , and the Ag 29 -Ag nanocluster was obtained via anchoring Ag + onto the Ag 29 nanocluster surface (see Experimental Method for more details).Only two Ag + ions could be introduced onto the nanocluster surface, while the Ag 29 (SSR) 12 -Ag x nanoclusters with x = 1, 3, 4 were absent.Such a tendency might result from the tunable chemical reactivity of the Ag 29 (SSR) 12 framework in reacting with the introduced Ag + ions.The bare Ag 29 (SSR) 12 could react with Ag + with a high degree of activity, while the Ag 29 -Ag showed no activity to further react with Ag + .That is, the addition of Ag + onto the Ag 29 (SSR) 12 framework might passivate the corresponding nanocluster.ESI-MS measurement was performed to determine the molecular formula of these Ag 29 nanoclusters (Fig. S1).The ESI-MS spectrum of Ag 29 -PPh 3 exhibited five separated signals, corresponding to the [Ag 29 (SSR) 12 (PPh 3 ) n ] 3− where n ranged from 0 to 4 (Fig. S1a,b).The existence of these five peaks was in agreement with the previously reported "dissociation-aggregation pattern " of the PPh 3 ligands in the nanocluster [49] .The mass spectrum of Ag 29 showed an intense mass peak that matched the [Ag 29 (SSR) 12 ] 3− .All PPh 3 ligands were dissociated from the Ag 29 surface after the DTAB addition since no peak of [Ag 29 (SSR) 12 (PPh 3 ) n ] 3− ( n = 1-4) was observed (Fig. S1c).The Ag 29 -Ag displayed two mass peaks, as shown in Fig. S1d, and the excellent match of the experimental and simulated isotope patterns demonstrated that these two peaks matched the [Ag 29 (SSR) 12 ] 3− and [Ag 29 (SSR) 12 -Ag] 2− , respectively.The mass signal of [Ag 29 (SSR) 12 -Ag] 2− verified the capture of Ag + onto the Ag 29 (SSR) 12 surface.However, the mass peak of [Ag 29 (SSR) 12 -Ag 2 ] 1− was absent, resulting from the weak interactions between the Ag 29 (SSR) 12 framework and Ag + ions.Besides, the PPh 3 dissociation among the conversion from Ag 29 -PPh 3 to Ag 29 and Ag 29 -Ag was further verified by the 31 P NMR measurement, where the 26.20 ppm signal of Ag 29 -PPh 3 disappeared in the latter two nanoclusters (Fig. S2).
The structural comparisons of these Ag 29 nanoclusters are shown in Fig. 1 and S2-S4.The Ag 29 -PPh 3 contained an icosahedral Ag 13 kernel that was stabilized by four Ag 3 (SR * ) 6 , where two SR * make up a SSR, to generate an Ag 25 (SSR) 12 framework.The four terminals of Ag 25 (SSR) 12 were further capped by Ag-PPh 3 units, giving rise to the overall structure of the highly symmetrical Ag 29 -PPh 3 ( Fig. 1 a and S3).Upon the DTABaddition induced conversion from Ag 29 -PPh 3 to Ag 29 , the PPh 3 ligands on the Ag 29 -PPh 3 surface were dissociated while the overall configuration of nanocluster remained highly symmetrical ( Fig. 1 b and S4).Such a PPh 3 dissociation was proposed to result from the competition effect between PPh 3 and DTAB -the PPh 3 ligands followed a "dissociationaggregation pattern " on the Ag 29 nanocluster surface [49] , while the presence of DTAB with a long carbon chain enabled the nanocluster surface to be fully covered and the dissociated PPh 3 could no longer be re-anchored onto the nanocluster vertex.Besides, the large steric hindrance of DTAB might also cause the PPh 3 dissociation in light of the steric effect in the nanocluster crystal lattice.Indeed, the Ag 29 nanocluster would maintain its framework, and no PPh 3 ligand was peeled off from the cluster surface when TMAB and TBAB surfactants with short carbon chains were introduced.Of note, such a bare Ag 29 structure has also been discovered in the presence of C 60 with a large steric (i.e., Ag 29 (SSR) 12 (C 60 ) n ) [50] .
Furthermore, the Ag + addition to the "bare " Ag 29 triggered the reprotection of partly exposed Ag sites (2/4; the 50% re-occupation) on the nanocluster surface, yielding the Ag 29 -Ag nanocluster ( Fig. 1 c and  S5).Significantly, because of the presence of the combined Ag + , Ag 29 -Ag displayed a symmetry-breaking construction.The Ag(cluster vertex) ••• Ag(combination) bond lengths were all around 2.77 Å, demonstrating its strong binding ability given that such lengths were close to the Ag(kernel) ••• Ag(icosahedral surface) bond lengths in the Ag 13 kernel of the nanocluster.The corresponding bond lengths among Ag 29 -PPh 3 , Ag 29 , and Ag 29 -Ag nanoclusters were further compared (Fig. S6).The average bond lengths of Ag(kernel) ••• Ag(icosahedral surface) in Ag 29 and Ag 29 -Ag were both lengthened relative to that of Ag 29 -PPh 3 with 0.98% and 0.76%, respectively (Fig. S6a).Besides, the average Ag(icosahedral surface) ••• Ag(icosahedral surface) bond lengths in Ag 29 -PPh 3 were increased by 2.06% and 0.76%, respectively, to Ag 29 and Ag 29 -Ag (Fig. S6b).In addition, the average Ag(icosahedral surface) ••• Ag(motif) bond length displayed a 1.03% elongation in both Ag 29 and Ag 29 -Ag compared with that of the Ag 29 -PPh 3 (Fig. S6c).Accordingly, both the icosahedral Ag 13 kernel and the Ag 25 (SSR) 12 framework were extended with the conversion from Ag 29 -PPh 3 to Ag 29 and Ag 29 -Ag.As for the interactions between the Ag vertex and the icosahedral Ag 13 , the average bond lengths in Ag 29 and Ag 29 -Ag were 3.058 and 3.151 Å, respectively (Fig. S6d, solid lines).However, no analogous interaction was perceived in Ag 29 -PPh 3 -distances between them (Fig. S6d, dotted lines) ranged from 3.493 to 3.643 Å (averagely, 3.523 Å).Consequently, the vertex Ag atoms became closer to the icosahedral Ag 13 kernel upon the conversion from Ag 29 -PPh 3 to both Ag 29 and Ag 29 -Ag, and the newly generated Ag 4 pyramid-like structures rendered the Ag 29 framework more robust [ 51 , 52 ].
The innermost icosahedral Ag 13 in the Ag 29 nanocluster was highly symmetrical, whereas the asymmetric arrangement of the surface "triskelion"-like Ag 4 (SR) 6 architectures rendered the chiral torsion of the overall cluster framework ( Fig. 1 ).For Ag 29 -PPh 3 , each crystal lattice was composed of eight Ag 29 cluster compounds, half of which were R -enantiomers while another half were S -enantiomers ( Fig. 1 a).In this context, the Ag 29 -PPh 3 crystal was racemic ( Fig. 2 a).The same phenomenon was observed in the Ag 29 crystal lattice ( Fig. 1   sequently, although both Ag 29 -PPh 3 and Ag 29 nanocluster crystals were highly emissive, their crystals were CD and CPL silent and optically inactive ( Fig. 2 e,f, black and red lines).

b and 2 b). Con-
Significantly, the Ag 29 -Ag nanocluster entities underwent chiral selfassembly with the crystallization process, which was reminiscent of the behavior of tartaric acids.Although the crystal lattice of Ag 29 -Ag contained both Ag 29 -Ag and Ag 29 cluster molecules, all these molecules were R -type (or S -type) enantiomers in the R -Ag 29 -Ag crystal (or S -Ag 29 -Ag crystal), as depicted in Fig. 1 c,d and 2 c,d.In this context, the crystals of R -Ag 29 -Ag and S -Ag 29 -Ag displayed intense CD and CPL signals and were highly optically active.Luo et al. reported that the addition of ligands to superatom structures could activate or passivate a nanocluster [58] .Herein, the combination of active-Ag site exposing induced by DCTB addition and the partly re-protecting induced by Ag + addition might activate the Ag 29 (SSR) 12 cluster framework to follow an asymmetrically crystallographic packing and display highly optical activities.As shown in Fig. 2  By comparison, the enantio-separated Ag 29 -PPh 3 nanocluster solutions displayed mirror image CD spectra at 460 nm with a dissymmetry factor of 1.5 × 10 − 3 , much higher than that of the crystal of R -Ag 29 -Ag and S -Ag 29 -Ag [47] .The CPL results of R -Ag 29 -Ag and S -Ag 29 -Ag crystals showed a single signal at 795 nm ( Fig. 2 f).The maximum | g lum | value of R -Ag 29 -Ag or S -Ag 29 -Ag crystals was determined to be approximately 5 × 10 − 2 (Fig. S10), much higher than those of the reported metal nanoclusters [54][55][56] , demonstrating the high optical activity of these nanocluster crystals.By comparison, the chiral Ag Upon the dissolution of the Ag 29 -Ag crystal, the CPL signal was disappeared (Fig. S11a), suggesting that the chirality tautomerism occurred in equilibrium.Inversely, the re-crystallization of the Ag 29 -Ag solution induced the chiral crystallographic self-assembly of cluster compounds that rendered the nanocluster CPL active again.Accordingly, the reversible transformation between the CPL-off solution and the CPL-on crystal of clusters has been accomplished (Fig. S11b).Because all solutions of Ag 29 -PPh 3 , Ag 29 , and Ag 29 -Ag were optically inactive, the generation of CPL was irrelevant to the PPh 3 dissociation, but was related to the Ag + combination.Besides, considering that the Ag + combination on the Ag 29 (SSR) 12 surface was not that robust (as evidenced by ESI-MS), we defined that the chiral self-assembly was mainly triggered by the Ag + combination among the cluster crystallization.Of note, the Nakashima group has reported the enantiomers of the Ag 29 -PPh 3 nanocluster by using high-performance liquid chromatography (HPLC) [47] .These Ag 29 -PPh 3 cluster molecules maintained their structures and compositions during the HPLC process.Compared with the HPLC technology, the crystallization-induced enantioseparation in this work was assigned to a chemical approach wherein the composition and configuration of the nanocluster were altered to a certain extent.
The DMF solutions of all Ag 29 nanoclusters exhibited almost the same optical absorptions with an intense peak at 445 nm and several shoulder bands at 320, 365, and 510 nm ( Fig. 3 a, solid lines); such similar absorptions demonstrated that the electronic orbits of clusters were mainly constituted by the Ag 29 (SSR) 12 framework, but were irrelevant to the surface PPh 3 or Ag stabilizers, which was reminiscent of the electronic properties of the Ag 29 (DHLA) 12 nanocluster [59] .Besides, the Ag 29 -PPh 3 and Ag 29 -Ag cluster solutions emitted at 640 nm, while the Ag 29 displayed photoluminescence (PL) at 633 nm ( Fig. 3 a, dotted lines).The Ag 29 -PPh 3 showed the strongest PL intensity among all Ag 29 clusters, and 3% and 12% reductions were detected by comparing the emission intensities of Ag 29 and Ag 29 -Ag, respectively, with that of Ag 29 -PPh 3 .
The optical absorptions and emissions of cluster crystalline films were further compared ( Fig. 3 b).The optical absorptions of all Ag 29 films were similar, whereas the 525 nm peak of Ag 29 was more intensive than those of other clusters ( Fig. 3 b, solid lines).The more pronounced absorption feature at 525 nm of the Ag 29 crystalline film might arise due to the intercluster close packing enhancing the excitations between the Ag 13 subunit and surface ligands [59] .Besides, a 10 nm red-shift was observed (i.e., 455 nm versus 445 nm) by comparing these absorptions with those of the cluster solutions.The emission wavelengths of cluster crystallized films displayed remarkable red-shifts relative to those of cluster solutions -Ag 29 -PPh 3 film emitted at 700 nm, Ag 29 film emitted at 707 nm, and Ag 29 -Ag film emitted at 652 nm ( Fig. 3 b, dotted lines).The significant shift in emissions between different forms was expected to result from a combined effect of the electronic coupling and of lattice-origin, non-radiative decay pathways occurring through electron-phonon interactions [ 48 , 60 , 61 ].In reference to the red-shift of emissions from the 700 nm of the Ag 29 -PPh 3 film to the 707 nm of the Ag 29 film, or the blue-shift to the 652 nm of the Ag 29 -Ag film, in addition to the aforementioned explanations, such a shift was also rationalized in terms of the different surface structures and crystalline packing modes among different Ag 29 nanoclusters [ 51 , 52 , 62 ].

Conclusion
In summary, a strategy termed "active-site exposing and partly re-protecting " was presented to trigger the symmetry breaking of highly symmetrical nanoclusters and the chiral self-assembly of cluster molecules in crystals, and to render these crystals highly optically active.The introduction of counterions with large steric hindrance dissociated the PPh 3 from the symmetrical Ag 29 (SSR) 12 (PPh 3 ) 4 nanocluster, and the vertex exposed Ag active sites of the nanoclusters was re-protected by Ag + , yielding an Ag 29 (SSR) 12 -Ag 2 nanocluster with a symmetry-breaking construction.The obtained Ag 29 (SSR) 12 -Ag 2 underwent chiral self-assembly with the crystallization process, and its crystal displayed strong optical activity, determined by both CD and CPL characterizations.Our work presents a new strategy for breaking the symmetry of highly symmetrical nanoclusters, inducing the enantioseparation of nanocluster racemates, and achieving strong optical activity of cluster-based nanomaterials.

Declaration of competing interest
The authors declare that they have no conflicts of interest in this work.
Scheme 1. Illustration of the "active-site exposing and partly re-protecting " strategy for triggering the symmetry breaking of highly symmetrical nanoclusters and rendering cluster crystals optically active.symmetrical nanoclusters and to render cluster crystals optically active ( Scheme 1 ).The Ag 29 (SSR) 12 (PPh 3 ) 4 (Ag 29 -PPh 3 for short; SSR = 1,3benzenedithiol) nanocluster was highly symmetrical with four Ag-PPh 3 vertex units.The introduction of counterions with large steric hindrance to the nanocluster system induced the dissociation of vertex PPh 3 and the generation of Ag 29 (SSR) 12 (Ag 29 for short) with exposed surface Ag active sites.Furthermore, the Ag + addition triggered the re-protection of partly exposed Ag sites on the Ag 29 nanocluster surface, yielding the Ag 29 (SSR) 12 -Ag 2 (Ag 29 -Ag for short) nanocluster with a symmetrybreaking construction.The cluster crystals of both Ag 29 -PPh 3 and Ag 29 clusters were racemic; by comparison, the crystallization of Ag 29 -Ag followed a chiral mode, accomplishing the enantioseparation of nanocluster racemates.Accordingly, the crystal of the symmetry-breaking Ag 29 -Ag cluster displayed strong optical activity, derived from CD and CPL characterizations.The DTAB addition-induced PPh 3 dissociation rendered vertex active Ag of the Ag 29 -PPh 3 nanocluster exploring, while the obtained Ag 29 cluster still adhered to the racemic crystallization.Besides, the Ag + addition triggered the re-protection of partly exposed Ag active sites and the symmetry breaking of the nanocluster, and the crystallization of Ag 29 -Ag cluster entities follows a chiral mode.
29 to Ag 29 (SSR) 12 -Ag 2 (Ag 29 -Ag) 30 mg of the Ag 29 crystal was dissolved in 10 mL of DMF, and 3 mg of CH 3 COOAg was added under vigorous stirring.After 30 min, the organic layer was separated and poured into 200 mL of CH 2 Cl 2 .The precipitate was collected to produce the Ag 29 -Ag nanocluster.The yield was 90% based on the Ag element (calculated from the Ag 29 ).Of note, the crystal analysis demonstrated that the Ag 29 -Ag crystal contained both Ag 29 -Ag and Ag 29 nanoclusters.The counterions of both Ag 29 and Ag 29 -Ag were DTAB.

Fig. 2 .
Fig. 2. Packing of Ag 29 nanocluster entities in the crystal lattice and the corresponding optical activity.(a) Crystal lattice of the racemic Ag 29 -PPh 3 nanoclusters with no optical activity.(b) Crystal lattice of the racemic Ag 29 nanoclusters with no optical activity.(c) Crystal lattice of chiral Ag 29 -Ag nanoclusters ( R enantiomer) with optical activity.(d) Crystal lattice of chiral Ag 29 -Ag nanoclusters (S enantiomers) with optical activity.The orange and blue labels of Ag 29 cluster entities represent their R and S enantiomerism, respectively.(e) CD spectra of different crystals of the Ag 29 series.(f) CPL spectra of different crystals of the Ag 29 series.
e and S9, R -Ag 29 -Ag and S -Ag 29 -Ag crystals exhibited mirror-image CD signals in the same wavelength region (i.e., at about 330 and 530 nm) with a dissymmetry factor of | g | = 7.0 × 10 − 4 .
29 nanoclusters protected by DHLA (dihydrolipoic acid) exhibited mirrored CPL signals at 660 nm with | g lum | value of 2 × 10 − 3 [57] .The differences of the CD signals between enantio-separated Ag 29 -PPh 3 solutions and chiral Ag 29 -Ag crystals as well as the CPL signals between chiral Ag 29 (DHLA) 12 solutions and chiral Ag 29 -Ag crystals might stem from two aspects: ( i , on the molecular level) their different molecular structures and surface chemistry and ( ii , on the supramolecular level) their different packing states and intercluster interactions.
All crystal structures were treated with PLATON SQUEEZE.The diffuse electron densities from these residual solvent molecules were removed.The CCDC number of the racemic Ag 29 (SSR) 12 nanocluster is 2071574.The CCDC number of the chiral Ag 29 (SSR) 12 -Ag 2 ( S enantiomer) nanocluster is 2071575.The CCDC number of the chiral Ag 29 (SSR) 12 -Ag 2 ( R enantiomer) nanocluster is 2071643.The CCDC number of Ag 29 (SSR) 12 (PPh 3 ) 4 in the presence of TMAB is 2150072.The CCDC number of Ag 29 (SSR) 12 (PPh 3 ) 4 in the presence of TBAB is 2150121.