Enantioselective Synthesis of Homochiral Au13 Nanoclusters and

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Enantioselective Synthesis of Homochiral Au13 Nanoclusters and Their Chiroptical Activities Yang Yang,*,† Qian Zhang,† Zong-Jie Guan,‡ Zi-Ang Nan,‡ Jia-Qi Wang,§ Tao Jia,† and Wen-Wen Zhan*,† †

Inorg. Chem. Downloaded from pubs.acs.org by WEBSTER UNIV on 03/01/19. For personal use only.

School of Chemistry and Material Science, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 221116, China ‡ College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China § Chemistry Department, Tsinghua University, Beijing 100084, China S Supporting Information *

ABSTRACT: A pair of enantiopure Au13 nanoclusters have been enantioselectively synthesized by chiral ligands with stereogenic centers at the phosphorus atoms. Their structures are determined by X-ray crystallography, which are typical models with a high symmetric core and chiral surface ligand arrangement. Correlation between the crystallographic structure, the calculation, and the circular dichroism (CD) study indicates that helical ligand arrangement inducing the core into chiral distortion accounts for the chiroptical activities in the visible region. A rare example of cocrystallization of a mixture of diastereomers has been observed for the first time for gold nanoclusters, reflecting the lack of chiral self-sorting of the ligands.

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and a chiral “footprint”,23 albeit they are still under debate. The atomically precise structural information is key to understanding the chiral origin. However, only three examples have been documented with crystallographic structures for chiralligand-protected pure gold nanoclusters.24 A BINAP-protected Au8 and a 1,4-bis(diphenylphosphino)-2,3-o-isopropylidene2,3-butanediol (DIOP)-protected Au11 were reported by Takano and Tsukuda.25 The optical activity in the visible region is believed to originate from a deformed gold core and further magnified by diffusion of π electrons of axial chiral binaphthyl groups. Very recently, an inherently chiral Au24 dictated by chiral 2,3-bis(diphenylphosphino)butane (dbpb; Chart 1) was presented by Konishi and co-workers. The origin was assigned to the helical gold framework.26 Despite recent progress, the origin of the chiroptical activity remains

INTRODUCTION Chirality is an important issue in nature. Many efforts have been made to understand chirality. In contrast to the wellstudied chiral organic compounds1 and chiral coordination polymers,2 chirality at nanoscale3,4 is still in its infancy, especially for gold nanoclusters,5 despite their promising applications in the fields of chiral sensing6 and catalysis.7 Structural information is important for understanding the structure−property relationship, and enantiopure nanoclusters are the key for applications. Although many atomically precise chiral gold nanoclusters have been synthesized, most of them are in racemic forms in the crystal lattice.8−12 Resolutions by chiral high-performance liquid chromatography (HPLC),13,14 chiral ammounium salts,15,16 and α-cyclodextrin17 have been successfully demonstrated. However, there are defects of resolutions such as sophisticated operation, low optical purity, risk of racemization,18 and a 50% maximum theoretical yield of the specified enantiomer.15 Enantioselective synthesis by a chiral ligand seems to be more efficient and enables us to probe the accurate structure as an enantiopure one. Indeed, chiral gold nanoclusters have been enantioselectively synthesized by applying chiral ligands such as L-glutahtione,19 20 D/L-penicillamine, and 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP).21 Chiroptical activities have been observed for these chiral gold clusters in metal-based transitions.19 Several mechanisms have been proposed to interpret the origin, such as an intrinsic chiral core, a dissymmetric field,22 © XXXX American Chemical Society

Chart 1. Ligands Discussed in the Text

Received: November 15, 2018

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DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ambiguous. More crystallographic structures are essential to fully picture the chiral origin of gold nanoclusters. The synthesis of enantiopure crystalline gold nanoclusters is challenging, and no chiral gold nanoclusters with a high symmetric core but pure helical organic ligand arrangement have been resolved or enantioselectively synthesized. High-symmetric icosahedral Au1327,28 is an important fundamental unit observed in many large nanoclusters.29−31 Nanocluster [Au 1 3 (dppe) 5 Cl 5 ] (dppe = 1,2-bis(diphenylphosphino)ethane; Chart 1), first reported by Shichibu and Konishi,32 is a typical model with a high symmetric core and chiral surface ligand arrangement. However, it is a racemic mixture that is unable to be resolved by chiral HPLC because of the fast racemization.33 Applying the enantiopure chiral ligand dbpb, which is a congener to dppe, in a similar synthesis procedure could not result in a crystalline product of Au13. The constraints imposed on the ethyl group by the steric hindrance of the two methyl substituents led to the preferential generation of Au24 clusters rather than Au13.26 On the basis of our previous work on the enantioselective synthesis of homochiral cluster compounds,6 we envision that the stereogenic moiety far away from the ligand backbone will have less impact for target structure formation. The chiral ligand 1,2-bis[(2-methoxyphenyl)phenylphosphino]ethane (L; Chart 1) is a good choice. The stereogenic center of this ligand is at the phosphorus atom because of the asymmetric attachment of methoxyl groups,34 in contrast to ligands with the chiral carbon moieties mentioned above (BINAP, DIOP, and dbpb). Herein, we report the successful enantioselective synthesis and full structural determination of a pair of enantiomerically pure Au13 clusters protected by L. The obtained homochiral Au13 clusters have slightly distorted icosahedral cores and helical surface ligand arrangements. To the best of our knowledge, they represent the first examples of enantiopure chiral gold nanoclusters with a high symmetric core and helical surface ligand arrangement, providing a good model for understanding both the influence of the chiral ligand arrangement on the core and the chiroptical origin.

Figure 1. (a) Crystal structure of the cation part of 1a with hydrogen omitted. (b) Top view of the core structures of 1a (left) and 1b (right), with bridged diphosphine (the dihedral angles between two gold atoms bridging with a ligand, labeled as α, and without a bridge, labeled as β). (c) Scheme of chiral core distortion with diphosphine (α < β). Color legend: golden, Au; pink, P; green, Cl; gray, C; red, O; white, H.

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configuration like ferrocene (Figure 1b,c). Five chiral diphosphine ligands with methoxyl groups hanging outward bridge the two rings in a propeller-like arrangement. The Au··· Au interactions between the two rings with bridged ligands are shorter than the contiguous unbridged ones. The dihedral angles between the planes of the gold atom from the Au5 rings and three axial gold atoms have been measured (Table S1). The dihedral angles between two gold atoms bridging with a ligand (labeled as α in Figure 1b,c) are always smaller than the adjacent ones without bridges (labeled as β in Figure 1b,c). There is clear structural evidence that the cluster core are slightly chiral distorted, induced by chiral ligand arrangement. The chiral arrangement of the five diphosphine ligands and core distortion break any inversion center and mirror reflection, reducing the chloride-ligated gold kernel from ideal D5d symmetry to chiral D5 symmetry (Figure 1c). The screw is anticlockwise, which could also be regarded as righthanded. All of the clusters in the crystal have the same handedness. When the chiral diphosphine is changed to its enantiomer (S)-L, [Au13(S)-L]5Cl2]Cl3 (1b) is obtained, which is crystallized in the chiral P3221 space group.35 1b is the enantiomer of 1a, with its chiral diphosphine ligands in a clockwise screw (left-handed, Figure 1b). The absolute configuration and enantiopurity of both crystal structures are

RESULTS AND DISCUSSION The synthesis of an enantiopure Au13 nanocluster adopts a method similar to the report by Shichibu and Konishi.32 Typically, to a dichloromethane solution containing L, Au(Me2S)Cl, and tetramethylammonium chloride was added slowly NaBH4 in an ethanol solution, followed by the addition of HCl in 2 h. After further reaction for 1 day, excess hexane was added to precipitate the crude product, which was washed by water, hexane, and Et2O, respectively. The pure crystalline samples were obtained by layering ether onto the methanol filtration in a thin tube in about 44% yield. Appling enantiopure dbpb instead of L under the same synthetic conditions could not lead to any crystallization product. The atomic structure information has been revealed by single-crystal X-ray structure determination. Upon application of enantiopure (R)-L, [Au13[(R)-L]5Cl2]Cl3 (1a) is obtained.35 Nanocluster 1a is crystallized in the chiral P3121 space group. The asymmetric unit contains one intact Au13 cluster and two independent half parts. As shown in Figure 1, the structure of 1a is similar to that of [Au13(dppe)5Cl5].32 The cluster kernel adopts an icosahedral configuration, with two chloride ligands coordinated to two polar axial positions. The two equatorial five-membered Au5 rings are in a staggered B

DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry supported by the Flack factors, which are close to zero, and circular dichroism (CD) studies (vide infra). The crystals studied are representative of the entire samples because they show CD signals identical with those of the bulk samples, ruling out the formation of conglomerates. The chiral configuration of nanocluster 1 is locked and dictated by the chirality of the chiral diphosphine ligands; i.e., (R)-L leads to a right-handed cluster and (S)-L results in a left-handed one, enabling the enantioselective synthesis of a homochiral Au13 nanocluster. The auxiliary methoxyl groups dissymmetrically linking two of the four phenyl rings of the ligand, which are stereogenic elements, favor a longer separated distance due to the steric strain, resulting in a preference for the ethyl group’s configuration. The configuration of the ethyl group is correlated to the handedness of the ligand arrangement on the Au13 surface (Figure S1). Compared with dbpb, which favors the generation of Au24,26 stereogenic methoxyl groups hanging outside are important for the formation of a homochiral Au13 nanocluster. The composition and formula have been verified by multiple techniques. A multicharged peak at m/z 1641.04 in the electrospray ionization mass spectrometry (ESI-MS) spectrum of 1a can be clearly assigned to [Au13(L)5Cl2]3+ (calcd m/z 1641.09), with well-matched shape and peak positions between the experimental and simulated isotope patterns (Figure S2). The thermogravimetric analysis (TGA) spectrum shows that the crystal samples contain lots of solvents, consistent with the large solvent-accessible voids found in the crystal lattice (Figures S3 and S4). The cluster is stable up to about 245 °C. The 49.1% weight loss of ligands is well agreed with the calculated value (formula [Au13(C28H28O2P2)5Cl5] contains 50.1% gold). X-ray photoelectron microscopy (XPS) analysis also confirmed the presence of gold, phosphorus, chlorine, oxygen, and carbon elements (Figure S5). The binding energy of Au 4f7/2 is determined to be 84.4 eV, which is close to the characteristics of Au 0 , comparable to the value of [Au13(dppe)5Cl5]. A total of 8 of the 13 gold atoms should have a valency of zero for charge balance. A singlet peak at 70.4 ppm in the 31P NMR spectrum of a CD2Cl2 solution of 1a indicates that the phosphines are in an identical environment, confirming its high symmetry and intactness in solution (Figure S6). The optical absorption spectrum of 1a shows two dominant peaks at 288 and 363 nm, with a broad band centered at 494 nm in the visible region (Figure 2). The profile is almost superimposable with the one of [Au13(dppe)5Cl5], meaning that both clusters share similar structures and the auxiliary methoxyl groups on the phenyl rings barely impact the electronic transitions. The optical energy band gap is calculated to be 1.80 eV (Figure S7). The successful enantioselective synthesis of a homochiral Au13 nanocluster is further confirmed by CD studies (Figure 2). 1a and 1b show perfect mirror images with respect to each other. The bisignate signals of the CD bands around 340−450 and 450−600 nm correspond to the dominant absorption peak at 363 nm and the band at 494 nm in the UV−vis spectrum, respectively. Compared with the same amount of ligands, which show CD signals in the 220−310 nm range (Figure S8), the intense signals of 1 above 340 nm are 2-fold amplified and should be induced Cotton effect. The absorption and CD spectra above 340 nm are well reproduced by time-dependent density functional theory (DFT) calculations (Figure 2c,d). According to the calculations (Figure S9), the band centered at

Figure 2. (a) CD spectra of 1a (black) and 1b (red) and the UV−vis spectrum of 1a in dichloromethane. (b) Corresponding anisotropy factors of 1a (black) and 1b (red). (c) Calculated absorption (red) and experimental (black) spectra. (d) Calculated CD (red) and experimental (black) spectra.

494 nm is mainly attributed to core-confined transitions, consistent with the previous report of [Au13(dppe)5Cl5].36 The peak at 363 nm primarily comes from transitions from the ligands to the cores, that is, a ligand-to-metal-charge-transfer process. On the basis of the calculations and crystal structures, CD bisignate signals around 340−450 nm are mainly contributed by the helical ligand arrangement. The Cotton effect in the range of 450−600 nm should have originated from chiral distortion of the core. The concentration-independent anisotropy factor (g = ΔA/A) is converted from CD spectra (Figure 2). The maximum appears at 408 nm, with g values reaching 1.6 × 10−3. Compared with other chiral-ligandprotected gold nanoclusters with crystallographic structures, this value is remarkably higher than Au11 without helical arrangement of the surface ligands but lower than Au8 with an axial chiral binaphthyl moiety25 and Au24 with an intrinsic chiral core.26 It should be noted that 1 has significant CD signals with g values up to 1.0 × 10−3 above 500 nm, in contrast to the recently reported optically pure chiral [Au13Cu2] nanocluster,37 containing the same icosahedral Au13 without core distortion, which is CD-silent above 500 nm. This clearly indicates the importance of the chiral distorted core for the chiral optical activities in the visible range attributed to a metal-based transition. No obvious change has been observed for the solution of 1a stored under ambient conditions in the absence of light for 1 month by monitoring its UV−vis spectra (Figure S10). The eight valence electrons of 1 agree with a typical closed electronic shell of a spherical superatom with a (1S)2(1P)6 configuration, which can explain its high stability. Keeping the solution of 1a at different temperatures of up to 50 °C for 15 min, their CD spectra have few changes in the 340−450 nm region but a more obvious decline in the range of 500−600 nm after heating at 40 °C (Figure 3). This means that the chiral arrangement of the ligands is retained, while the gold core is fluxional38 and its chiral distortion tends to relax at elevated temperature. However, the spectrum of 1a after heating at 50 °C for 1 h remains the same (Figure S11), indicating that there is no racemization. Very interestingly, when a racemic ligand is applied in the synthesis, crystalline samples (2) are also obtained in high yield similar to the enantiopure ones. The crystals are CDC

DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

the gold surface when they are present in the enantiopure form.

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CONCLUSION In summary, we have successfully enantioselectively synthesized and structurally characterized a pair of enantiomerically pure Au13 clusters, which indicate the importance of the positions of the stereogenic methoxyl groups hanging outward. The present homochiral Au13 nanocluster is a typical model with a symmetric core and pure chiral surface ligand arrangement. The chirality of the helical arrangement of the surface ligands is dictated by the chirality of the chiral diphosphine ligands, enabling enantioselective synthesis. The crystal structures clearly show the gold core in a chiral distortion induced by chiral arrangement of the surface ligands, which is responsible for the chiroptical activity in a metal-based transition. An interesting and rare example of crystallization of a mixture of diastereomers reflects the lack of chiral self-sorting of the ligand. The high yield, stability, and chiral persistence of the clusters facilitate their promise in applications such as chiral catalysis in future.

Figure 3. CD spectra of 1a after heating at different temperatures for 15 min.

silent, and their UV−vis spectrum is similar to that of 1. X-ray structural determination reveals that 2 is crystallized in the I4̅2d space group, which is an achiral space group. This is an interesting example of cocrystallization of a mixture of diastereomers of [Au13L5Cl2]Cl3,35 which is first observed in gold cluster compounds. The asymmetric unit consists of half of a Au13 cluster. Two well-defined ligands and half of a ligand with auxiliary methoxyl groups disorderly occupied at two positions of two phenyl rings are clearly defined in the asymmetric unit cell (Figure S12). Thus, there are clusters with four (S)-L and one (R)-L in one cluster, mixing with homochiral ones [five (S)-L] due to the disorder of one of the ligand’s auxiliary methoxyl groups (Figure 4), and their

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EXPERIMENTAL SECTION

General Method. CD spectra were measured using a Jasco J-810 spectrodichrometer. UV−vis spectra were recorded on a Beijing Xipu spectrophotometer. NMR data were obtained by Bruker Avance II spectrometers (400 MHz and 600 MHz). Mass spectrometry (MS) was performed with a Bruker micro-TOF-QII mass spectrometer (ESI-TOF). TGA spectra were recorded on a TGA Q50 analyzer. XPS data were recorded on a Thermo ESCALAB 250XI spectrometer. All reagents employed were commercially available and used without further purification. The solvents used were of analytical grade. Chiral 1,2-bis[(2-methoxyphenyl)phenylphosphino]ethane was obtained from Alfa Aesar. Syntheses. Synthesis of 1a. To 3 mL of a dichloromethane solution containing (R)-2-bis[(2-methoxyphenyl)phenylphosphino]ethane [(R)-L; 20 mg, 0.044 mol] was added Au(Me2S)Cl (25.7 mg 0.088 mol). The mixture was stirred for 20 min before the addition of 11.2 μL (0.088 mol) of tetramethylammonium chloride. After stirring for another 15 min, 4 mL of an ethanol solution of NaBH4 (3.3 mg 0.088 mol) was added dropwise. The solution turned dark red and was kept stirring at room temperature for 2 h, followed by the addition of 96 μL of a 12 M HCl solution. After stirring for 24 h, excess hexane was added to the solution. The reddish-black oily precipitate was washed with pure water, hexane, and Et2O, respectively. The resulting solid was dissolved in methanol and filtered. After 2 weeks, black crystals were obtained by layering ether on the filtrate in a thin tube at 4 °C. Yield: 15 mg, ca. 44.4%, based on gold. 31P NMR: δ 70.41. ESI-MS. Calcd for [Au(L)5Cl2]3+: m/z 1641.04. UV−vis (λ, nm): 288, 363, 494. XPS (binding energy, eV): Au 4f7/2, 84.4; Au 4f5/2, 88.1. The synthesis of 1b and 2 shared the same process as that of 1a but instead using (S,S)-1,2-bis[(2methoxyphenyl)phenylphosphino]ethane and racemic 1,2-bis[(2methoxyphenyl)phenylphosphino]ethane, respectively. X-ray Crystallography. Diffraction data were collected on an Agilent SuperNova X-ray diffractometer at 100 K using microfocus Xray sources (Cu Kα, λ = 1.54184 Å for 1a, 1b, and 2). The crystals were fragile and easily lost solvent molecules. TGA spectra of crystalline samples (Figure S4) confirmed that they had lots of cocrystallized solvents. Thus, rapid handling of the samples was needed. Absorption corrections were applied by using the program CrysAlis (multiscan). Using Olex2,41 the structures were solved with the ShelXT42 structure solution program using Intrinsic Phasing and refined with the ShelXL or XH refinement package using least-squares minimization. Non-hydrogen atoms except counteranions and some disordered parts of auxiliary methoxyl groups were refined anisotropically by least squares on F2. The hydrogen atoms of the organic

Figure 4. Crystal structures of the cation part of (a) [Au13[(S)L]4[(R)-L]Cl2]Cl3 and (b) 1b in 2. They are different in the methoxyl groups of L highlighted in ball mode in black cycles. This situation is due to the disordered occupation of methoxyl groups at two positions in the asymmetric unit.

enantiomers are generated by crystal symmetry operations. Thus, the whole crystal is a mixture of diastereomers. As for the chiral arrangement of ligands on the cluster, left- and righthanded ones are present in equivalent amounts. The chiral helical arrangement is dictated by the chirality of the majority. For example, [Au13[(S)-L]4[(R)-L]Cl2]Cl3 is right-handed, the same as 1b. There is a lack of absolute homo39/heterochiral40 self-sorting, which is also verified by the unresolvable complicated signals in 1H NMR, in contrast to the simple ones of homochiral 1, indicating lower symmetry (Figure S13). The mixture of diastereomers of 2 is easily recrystallized after dissolution, hinting that the methoxyl groups which determine the chirality of the ligands and further chiral arrangement of the ligands on the cluster have limited influence on the crystal packing. The constraints imposed by the chiral moiety to the ethyl group are not significant enough to induce homochiral self-sorting; i.e., all homochiral ligands are sorted into one cluster without a heterochiral one. However, at least they are sufficient enough to stereocontrol the chiral arrangement on D

DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ligands were generated geometrically. Because of the large unit cells and small sizes of the crystals, the diffractions were relatively weak. Not all of the counteranions (Cl−) were found because of the weak data and high symmetry. The correct chemical formula reported in the crystallographic data took the undefined counterions into consideration for charge balance. The crystals had large solventaccessible voids because a large number of disordered solvent molecules and counteranions (Cl−) were not resolved. Thus, SQUEEZE routines43 in PLATON were employed in the structural refinement. The detailed structure data are available at the Cambridge Crystallographic Data Centre as CCDC 1876610−1876612. Calculations. DFT calculations were performed with the quantum chemistry program Gaussian 09. The 6-31G* basis set was used for carbon, oxygen, phosphorus, chlorine, and hydrogen and LANL2dz for gold.44,45 Structural optimization was not performed in the calculation. Time-dependent DFT calculations of UV−vis absorption were done with the functions of CAM-B3LYP.46 A total of 100 singlet states (nstates = 100, singlet) were chosen in the calculations of the UV−vis absorption spectra. The calculated absorption spectroscopy and CD analyses were performed by Multiwfn.

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(4) Zhu, Z.; Liu, W.; Li, Z.; Han, B.; Zhou, Y.; Gao, Y.; Tang, Z. Manipulation of Collective Optical Activity in One-Dimensional Plasmonic Assembly. ACS Nano 2012, 6, 2326. (5) Jin, R.; Zhu, Y.; Qian, H. Quantum-sized gold nanoclusters: bridging the gap between organometallics and nanocrystals. Chem. Eur. J. 2011, 17, 6584. (6) Yang, Y.; Pei, X. L.; Wang, Q. M. Postclustering dynamic covalent modification for chirality control and chiral sensing. J. Am. Chem. Soc. 2013, 135, 16184. (7) Oila, M. J.; Koskinen, A. M. P. Chirally modified gold nanoparticles: nanostructured chiral ligands for catalysis. ARKIVOC 2006, XV, 76. (8) Wan, X.-K.; Yuan, S.-F.; Lin, Z.-W.; Wang, Q.-M. A Chiral Gold Nanocluster Au20 Protected by Tetradentate Phosphine Ligands. Angew. Chem., Int. Ed. 2014, 53, 2923. (9) Zeng, C.; Li, T.; Das, A.; Rosi, N. L.; Jin, R. Chiral structure of thiolate-protected 28-gold-atom nanocluster determined by X-ray crystallography. J. Am. Chem. Soc. 2013, 135, 10011. (10) Jadzinsky, P. D.; Calero, G.; Ackerson, C. J.; Bushnell, D. A.; Kornberg, R. D. Structure of a Thiol Monolayer-Protected Gold Nanoparticle at 1.1 Å Resolution. Science 2007, 318, 430. (11) Zeng, C.; Chen, Y.; Kirschbaum, K.; Lambright, K. J.; Jin, R. Emergence of hierarchical structural complexities in nanoparticles and their assembly. Science 2016, 354, 1580. (12) Chen, J.; Zhang, Q.-F.; Williard, P. G.; Wang, L.-S. Synthesis and Structure Determination of a New Au20 Nanocluster Protected by Tripodal Tetraphosphine Ligands. Inorg. Chem. 2014, 53, 3932. (13) Knoppe, S.; Dolamic, I.; Dass, A.; Bürgi, T. Separation of Enantiomers and CD Spectra of Au40(SCH2CH2Ph)24: Spectroscopic Evidence for Intrinsic Chirality. Angew. Chem., Int. Ed. 2012, 51, 7589. (14) Dolamic, I.; Knoppe, S.; Dass, A.; Bü r gi, T. First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands. Nat. Commun. 2012, 3, 798. (15) Yan, J.; Su, H.; Yang, H.; Hu, C.; Malola, S.; Lin, S.; Teo, B. K.; Häkkinen, H.; Zheng, N. Asymmetric Synthesis of Chiral Bimetallic [Ag28Cu12(SR)24]4− Nanoclusters via Ion Pairing. J. Am. Chem. Soc. 2016, 138, 12751. (16) Knoppe, S.; Wong, O. A.; Malola, S.; Häkkinen, H.; Bürgi, T.; Verbiest, T.; Ackerson, C. J. Chiral Phase Transfer and Enantioenrichment of Thiolate-Protected Au102 Clusters. J. Am. Chem. Soc. 2014, 136, 4129. (17) Zhu, Y.; Wang, H.; Wan, K.; Guo, J.; He, C.; Yu, Y.; Zhao, L.; Zhang, Y.; Lv, J.; Shi, L.; Jin, R.; Zhang, X.; Shi, X.; Tang, Z. Enantioseparation of Au20(PP3)4Cl4 Clusters with Intrinsically Chiral Cores. Angew. Chem., Int. Ed. 2018, 57, 9059. (18) Knoppe, S.; Dolamic, I.; Bürgi, T. Racemization of a Chiral Nanoparticle Evidences the Flexibility of the Gold−Thiolate Interface. J. Am. Chem. Soc. 2012, 134, 13114. (19) Schaaff, T. G.; Whetten, R. L. Giant Gold−Glutathione Cluster Compounds: Intense Optical Activity in Metal-Based Transitions. J. Phys. Chem. B 2000, 104, 2630. (20) Yao, H.; Miki, K.; Nishida, N.; Sasaki, A.; Kimura, K. Large Optical Activity of Gold Nanocluster Enantiomers Induced by a Pair of Optically Active Penicillamines. J. Am. Chem. Soc. 2005, 127, 15536. (21) Yanagimoto, Y.; Negishi, Y.; Fujihara, H.; Tsukuda, T. Chiroptical Activity of BINAP-Stabilized Undecagold Clusters. J. Phys. Chem. B 2006, 110, 11611. (22) Yao, H. Chiral ligand-protected gold nanoclusters: Considering the optical activity from a viewpoint of ligand dissymmetric field. Prog. Nat. Sci. 2016, 26, 428. (23) Gautier, C.; Bürgi, T. ChiralN-Isobutyryl-cysteine Protected Gold Nanoparticles: Preparation, Size Selection, and Optical Activity in the UV−vis and Infrared. J. Am. Chem. Soc. 2006, 128, 11079. (24) The crystallographic structures of a pair of ultrasmall molecular Au3 clusters with chiral ligands were also reported. Shi, L.; Zhu, L.; Guo, J.; Zhang, L.; Shi, Y.; Zhang, Y.; Hou, K.; Zheng, Y.; Zhu, Y.; Lv, J.; Liu, S.; Tang, Z. Self-Assembly of Chiral Gold Clusters into

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03171. Dihedral angles, configuration of the ligands, ESI-MS, TGA, XPS, NMR, and UV−vis spectra, packing mode and optical energy band gap of 1a, comparison of CD spectra, Kohn−Sham orbital energy levels and electronic diagrams, and asymmetric unit of the crystal structure of 2 (PDF) Accession Codes

CCDC 1876610−1876612 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yang Yang: 0000-0003-4888-1604 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant 21701064), Natural Science Foundation of Jiangsu Province (Grant BK20170230), and Foundation of Jiangsu Normal University (Grant 16XLR014).

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REFERENCES

(1) Barron, L. D. SYMMETRY AND MOLECULAR CHIRALITY. Chem. Soc. Rev. 1986, 15, 189. (2) Yoon, M.; Srirambalaji, R.; Kim, K. Homochiral metal-organic frameworks for asymmetric heterogeneous catalysis. Chem. Rev. 2012, 112, 1196. (3) Li, Z.; Zhu, Z.; Liu, W.; Zhou, Y.; Han, B.; Gao, Y.; Tang, Z. Reversible Plasmonic Circular Dichroism of Au Nanorod and DNA Assemblies. J. Am. Chem. Soc. 2012, 134, 3322. E

DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Crystalline Nanocubes of Exceptional Optical Activity. Angew. Chem., Int. Ed. 2017, 56, 15397. (25) Takano, S.; Tsukuda, T. Amplification of the Optical Activity of Gold Clusters by the Proximity of BINAP. J. Phys. Chem. Lett. 2016, 7, 4509. (26) Sugiuchi, M.; Shichibu, Y.; Konishi, K. An Inherently Chiral Au24 Framework with Double-Helical Hexagold Strands. Angew. Chem., Int. Ed. 2018, 57, 7855. (27) Briant, C. E.; Theobald, B. R. C.; White, J. W.; Bell, L. K.; Mingos, D. M. P.; Welch, A. J. Synthesis and X-ray structural characterization of the centred icosahedral gold cluster compound [Aul3(PMe2Ph)10Cl2](PF6)3; the realization of a theoretical prediction. J. Chem. Soc., Chem. Commun. 1981, 201. (28) Zhang, S.-S.; Feng, L.; Senanayake, R. D.; Aikens, C. M.; Wang, X.-P.; Zhao, Q.-Q.; Tung, C.-H.; Sun, D. Diphosphine-protected ultrasmall gold nanoclusters: opened icosahedral Au13 and heartshaped Au8 clusters. Chem. Sci. 2018, 9, 1251. (29) Zhu, M.; Aikens, C. M.; Hollander, F. J.; Schatz, G. C.; Jin, R. Correlating the Crystal Structure of A Thiol-Protected Au25 Cluster and Optical Properties. J. Am. Chem. Soc. 2008, 130, 5883. (30) Wan, X. K.; Cheng, X. L.; Tang, Q.; Han, Y. Z.; Hu, G.; Jiang, D. E.; Wang, Q. M. Atomically Precise Bimetallic Au19 Cu30 Nanocluster with an Icosidodecahedral Cu30 Shell and an AlkynylCu Interface. J. Am. Chem. Soc. 2017, 139, 9451. (31) Song, Y.; Fu, F.; Zhang, J.; Chai, J.; Kang, X.; Li, P.; Li, S.; Zhou, H.; Zhu, M. The Magic Au60 Nanocluster: A New ClusterAssembled Material with Five Au13 Building Blocks. Angew. Chem., Int. Ed. 2015, 54, 8430. (32) Shichibu, Y.; Konishi, K. HCl-induced nuclearity convergence in diphosphine-protected ultrasmall gold clusters: a novel synthetic route to ″magic-number″ Au13 clusters. Small 2010, 6, 1216. (33) Zhang, J.; Zhou, Y.; Zheng, K.; Abroshan, H.; Kauffman, D. R.; Sun, J.; Li, G. Diphosphine-induced chiral propeller arrangement of gold nanoclusters for singlet oxygen photogeneration. Nano Res. 2018, 11, 5787. (34) Knowles, W. S. Asymmetric Hydrogenations (Nobel Lecture). Angew. Chem., Int. Ed. 2002, 41, 1998. (35) (a) Crystal data for 1a: C140H140Au13Cl5O10P10, a = 31.75060(10) Å, b = 31.75060(10) Å, c = 78.7289(3) Å, α = 90.00°, β = 90.00°, γ = 120.00°, V = 68733.5(4) Å3, trigonal space group P3121, Z = 12, T = 100 K, 407265 reflections measured, 78280 unique (Rint = 0.0752), final R1 = 0.0797, wR2 = 0.1929 for 66798 observed reflections [I > 2σ(I)]. Flack factor = −0.021(14). (b) Crystal data for 1b: C140H140Au13Cl5O10P10, a = 32.12170(10 Å, b = 32.12170(10) Å, c = 79.1092(3) Å, α = 90.00°, β = 90.00°, γ = 120.00°, V = 70689.4(5) Å3, trigonal space group P3221, Z = 12, T = 100 K, 690398 reflections measured, 98790 unique (Rint = 0.0868), final R1 = 0.0584, wR2 = 0.1707 for 75985 observed reflections [I > 2σ(I)]. Flack factor = −0.027(4). (c) Crystal data for 2: C140H140Au13Cl5O10P10, a = 31.4316(5) Å, b = 31.4316(5) Å, c = 46.5012(18) Å, α = 90°, β = 90°, γ = 90°, V = 45941(2) Å3, tetragonal space group I4̅2d, Z = 8, T = 100 K, 49539 reflections measured, 21169 unique (Rint = 0.0440), final R1 = 0.0800, wR2 = 0.2196 for 18161 observed reflections [I > 2σ(I)]. (36) Sugiuchi, M.; Shichibu, Y.; Nakanishi, T.; Hasegawa, Y.; Konishi, K. Cluster-pi electronic interaction in a superatomic Au13 cluster bearing sigma-bonded acetylide ligands. Chem. Commun. 2015, 51, 13519. (37) Deng, G.; Malola, S.; Yan, J.; Han, Y.; Yuan, P.; Zhao, C.; Yuan, X.; Lin, S.; Tang, Z.; Teo, B. K.; Hakkinen, H.; Zheng, N. From Symmetry Breaking to Unraveling the Origin of the Chirality of Ligated Au13Cu2 Nanoclusters. Angew. Chem., Int. Ed. 2018, 57, 3421. (38) Provorse, M. R.; Aikens, C. M. Origin of Intense Chiroptical Effects in Undecagold Subnanometer Particles. J. Am. Chem. Soc. 2010, 132, 1302. (39) Hutin, M.; Cramer, C. J.; Gagliardi, L.; Shahi, A. R. M.; Bernardinelli, G.; Cerny, R.; Nitschke, J. R. Self-Sorting Chiral Subcomponent Rearrangement During Crystallization. J. Am. Chem. Soc. 2007, 129, 8774.

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DOI: 10.1021/acs.inorgchem.8b03171 Inorg. Chem. XXXX, XXX, XXX−XXX