Chiroptical Activity Enhancement via Structural Control: The Chiral Synthesis and Reversible Interconversion of Two Intrinsically Chiral Gold Nanoclusters

Article abstract of DOI:10.1021/jacs.8b11096

We report the synthesis and crystal structure determination of two novel chiral gold nanoclusters. By utilizing BINAP, we isolate atomically precise intrinsically chiral Au nanoclusters [Au₉(R-/S-BINAP)₄](CF₃COO)₃ and [Au₁₀(R-/S-BINAP)₄(p-CF₃C₆H₄C=C)](CF₃COO)₃ in high yield with one-pot synthesis. Au₉ has C₂ geometry, while Au₁₀ is C₁ symmetric. Interestingly, reversible interconversion between Au₉ and Au₁₀ can be realized by the addition or removal of a RC=CAu component. The transformation from Au₉ to Au₁₀ leads to significant enhancement of CD signals. The maximum anisotropy factor in the visible region of [Au₁₀(BINAP)₄(p-CF₃C₆H₄C=C)]³⁺ is the hitherto largest (up to 6.6 × 10^-3) among gold nanoclusters, which is approximately twice of that of [Au₉(BINAP)₄]³⁺. This work demonstrates that the chiroptical activity of gold nanoclusters can be modulated by structural control through the introduction of second ligands.

Full text of DOI:10.1021/jacs.8b11096

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Article
Chiroptical Activity Enhancement via Structural Control: the Chiral Syn-thesis
and Reversible Interconversion of Two Intrinsically Chiral Gold Nanoclusters
Jia-Qi Wang, Zong-Jie Guan, Wen-Di Liu, Yang Yang, and Quan-Ming Wang
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 18 Jan 2019
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Journal of the American Chemical Society
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Chiroptical Activity Enhancement via Structural Control: the
Chiral Synthesis and Reversible Interconversion of Two In-
trinsically Chiral Gold Nanoclusters
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†
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, $
, †,‡
‡
Jia-Qi Wang, Zong-Jie Guan, Wen-Di Liu, Yang Yang* and Quan-Ming Wang*
† Department of Chemistry, Tsinghua University, Beijing 10084, PR China
‡ Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen, 361005, PR China
$ School of Chemistry and Materials Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu, PR China
Supporting Information Placeholder
ABSTRACT: We report the synthesis and crystal structure determination of two novel chiral gold nanoclusters. By utilizing BINAP,
we isolate atomically precise intrinsically chiral Au nanoclusters [Au9(R- / S-BINAP)4](CF3COO)3 and [Au10(R- / S-BINAP)4(p-
CF3C6H4C≡C)](CF3COO)3 in high yield with one-pot synthesis. Au9 has C2 geometry while Au10 is C1 symmetric. Interestingly,
reversible interconversion between Au9 and Au10 can be realized by the addition or removal of a RC≡CAu component. The transfor-
mation from Au9 to Au10 leads to significant enhancement of CD signals. The maximum anisotropy factor in the visible region of
[Au10(BINAP)4(p-CF3C6H4C≡C)]3+ is the hitherto largest (up to 6.6 * 10-3) among gold nanoclusters, which is approximately twice
of that of [Au9(BINAP)4]3+. This work demonstrates that chiroptical activity of gold nanoclusters can be modulated by structural
control through the introduction of second ligands.
INTRODUCTION
Chiral materials are of great interest for their promising appli-
cations in medicine design, biorecognition, enantioselective ca-
talysis, optical devices, holography, chiral sensing and isola-
tion.1-8 Among chiral nanomaterials, ligand-protected chiral
coinage metal nanoclusters with atomic precision attracted re-
cent attention,9-25 because chiral nanoclusters with well-defined
structures are advantages in correlating the chirality with
nanocluster size and surface properties.12-15 The understanding
and application of the optical characteristics of chiral gold clus-
ters remains a great challenge due to rare structural evidences
of enantiomerically pure Au clusters.15, 20
Chart 1. Phosphine ligands employed in the present study.
Chiral metal clusters can be sorted into three categories:17, 18
(i) the structure of the metal skeleton is intrinsically chiral; (ii)
an inherently achiral core with a chiral shell generated from the
symmetric arrangement of surface-protecting units; (iii) chiral
ligands induce chiroptical properties of Au nanoclusters
through vicinal effects or through a chiral electrostatic field.16,
26-30 For the second category, racemic mixtures are produced, so
enantioseparation of Au nanoclusters has been carried out by
using chiral HPLC columns (Au28,26 Au3831) and phase transfer
method with chiral ammonium salts (Au11,32 Au10233). It is in-
convenient and time-consuming to employ chiral HPLC col-
umns to separate the as-prepared racemic mixture into enantio-
mers. Although an ion-pairing strategy was used for direct
asymmetric synthesis of optically active nanoparticles, this
method requires the design of chiral counterions and is imprac-
tical when the Au nanoclusters are neutral. Thus, chiral ligand
induction provides a practical and straightforward protocol for
the synthesis of chiral Au nanoclusters.15, 20, 30, 34-36
So far, structural evidences for gold nanoclusters with chiral
ligands remain relatively scarce. 15, 36 There are only three ex-
amples with determined structures by X-ray diffraction:
15
[Au11(R-/S-DIOP)4Cl2]Cl, [Au8(R-/S-BINAP)3(PPh3)2](PF6)2
and [Au24L6Cl4]Cl2 (L = (R,R)- and (S,S)-2,3-bis(diphe-
nylphosphino)butane).36 In our previous work, we achieved the
introduction of alkynyl ligands into the protecting sphere of
metal nanoclusters and obtained atomically precise nanol-
custers [Au19(PhC≡C)9(Hdppa)3](SbF6)2 (Hdppa = N,N-bis(di-
phenylphosphino)amine),
[Au23(PhC≡C)9(PPh3)6](SbF6)2,
[Au24(PhC≡C)14(PPh3)4](SbF6)2,
[Au40(PhC≡C)20(dppm)4](SbF6)4
and
[Au10Ag2(2-py-
C≡C)3(dppy)6](BF4)5.37-42 Taking advantage of this direct re-
duction strategy of preparing mixed-ligand protected Au
nanoclusters, we utilized (R)- and (S)- 2 , 2′- bis - (diphe-
nylphosphino)-1,1’-binaphthyl ((R)- and (S)-BINAP) (Chart 1)
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should display 8 peaks at the same ratio based on the number of
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in order to induce the formation of chiral pure gold nanoclus-
ters with intrinsic chiral metal cores. We managed to isolate two
pairs of chiral gold nanoclusters, namely [Au9(R-/S-
BINAP)4](CF3COO)3 ((R)-Au9/(S)-Au9) and [Au10(R-/S-
BINAP)4(p-CF3C6H4C≡C)](CF3COO)3 ((R)-Au10/(S)-Au10).43
Herein, we report their asymmetric synthesis and crystal struc-
tures as well as the reversible interconversion between Au9 and
Au10. It is noteworthy that Au10 show a large g value (up to 6.6
* 10-3), which is the largest among reported chiral gold
nanoclusters so far.31
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atoms of each type. Experimentally, eight peaks at δ = 29.23,
48.02, 50.84, 52.13, 57.51, 64.45 and 69.73 ppm were observed
in a ratio of 1:1:1:1:1:1:2 (Supporting Information, Figure S3).
The peak at δ= 69.73 ppm with two fold abundance indicates
that phosphorous donors (types G and H) are linked to two types
of Au atoms with similar coordination environments (Figure
2b). The 31P NMR spectra provide strong evidence for support-
ing that the symmetry and structures of Au9 and Au10 are re-
tained in solution (Figure 2b). It is noteworthy that P^P-Au-
C≡CR motif is formed in Au10 due to the involvement of the
binding of RC≡C, and this motif can be viewed as a semi-staple,
which is different from the previous reported staple motif
RC≡C-Au-C≡CR.37-41
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RESULT AND DISCUSSION
Synthesis and Characterization. To prepare (R)-Au9,
a
CH2Cl2 solution containing o-CF3C6H4C≡CAu and (R)-BINA-
PAu2(CF3COO)2 was reduced by NaBH4 (Method 1). Similarly,
(S)-Au9 can be synthesized by using (S)-BINAPAu2(CF3COO)2.
o-CF3C6H4C≡C ligands were not in the product Au9 due to ste-
ric factor. Therefore the reaction was repeated without o-
CF3C6H4C≡CAu precursor, i.e. direct reduction of (R)- or (S)-
BINAPAu2(CF3COO)2 gave rise to homoleptic phosphine-pro-
tected Au9 (Method 2, Figure S1). (R)-Au10 and (S)-Au10 were
prepared from the reduction of p-CF3C6H4C≡CAu and (R)- or
(S)-BINAPAu2(CF3COO)2 by NaBH4 in CH2Cl2, respectively.
Dark red crystals of Au9 and Au10 were grown by layering n-
hexane : ether (V : V=1 : 1) onto the filtrate of the reaction mix-
ture. Similar synthetic procedures gave different products.
Single-crystal structural analysis revealed that (R)-Au9 /(S)-
Au9 and (R)-Au10 / (S)-Au10 comprise tricationic clusters
[Au9(R-/S-BINAP)4]3+
and
[Au10(R-/S-BINAP)4(p-
CF3C6H4C≡C)]3+, respectively (Figure 1). For better under-
standing the structures, the anatomy illustration is shown in Fig-
ure 2. The core of (R)-Au9 or (S)-Au9 is composed of two Au4
tetrahedra sharing a common Au atom, and two additional Au
atoms are attached from the opposite side (Figure 2a). The Au9
core has a C2 symmetry with a twofold axis passing through
Au9 and the middle point between Au1 and Au2. The skeleton
is different from the reported butterfly [Au9(PPh3)8]3+ with D2h
symmetry.44 However, the Au9 core can be viewed as a distorted
crown structure, which is somewhat similar to the crown
[Au9{P(C6H4OMe-p)3}8]3+ with D4d symmetry. 45, 46 Au10 has an
exterior Au atom attaching on one of the corner of a tetrahedron
with the Au-Au distance of 2.953 Å, which leads to a very low
symmetry (C1). It is also interesting to compare the
[Au10(BINAP)4(p-CF3C6H4C≡C)]3+cluster with a very different
Figure 1. Total X-ray crystal structure of the tricationic cluster
(R)-Au9/(S)-Au9 and Au10/(S)-Au10. Au, orange; P, pink; C, grey.
All hydrogen atoms and –CF3 units are omitted for clarity.
Au10
structure
from
[Au10(C6F5)4(PPh3)5],47
[Au10(PPh3)7{S2C2(CN)2}2],48 [Au10Cl3(PCy2Ph)6](NO3)49 and
K[Au(AuCl)(AuPPh3)8)](PF6)2.50 The Au-Au distances from
the Au atoms of the kernels are different between Au9 and Au10.
In the kernel of Au9, the Au-Au distances are in the range of
2.6544(16)–2.9560(17) Å. The Au–Au distances from the Au
atoms of Au10 are in the range of 2.632(3)–3.3860(39) Å. As
illustrated in Figure 2b, the addition of the RC≡CAu component
causes the increase of the distances of Au1-Au3 (from
2.9244(16) to 3.3026(66)) and Au2-Au4 (from 2.9560(17) to
3.3860(39)). The P^P-Au-C≡CR staple is different from the
previous staple motif previously reported (Figure 2c).37-42 The
P^P-Au-C≡CR motif has a linear pattern where the RC≡C-
ligands are almost in line with the Au-P bonds.
(a)
In solution, the 31P NMR of Au9 displays four peaks at δ =
53.29, 54.27, 56.25 and 74.93 ppm in a 1 : 1 : 1 : 1 ratio, which
is in accordance with its two fold symmetry (C2) (Supporting
Information, Figure S2). In Au10, the symmetry is lowered com-
pared to Au9 due to the asymmetrically addition of the p-
CF3C6H4C≡CAu unit. Consequently, the 31P NMR of Au10
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(a)
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(b)
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(c)
Figure 2. (a) Au9 and Au10 cores. (b) The arrangement of BINAP
ligands in (R)-Au9/(S)-Au9 and (R)-Au10/(S)-Au10. (c) Reported
staple motifs in gold–alkynyl or gold–alkynyl-phosphine systems.
Au, orange; P, pink; C, grey. Blue curve: binaphthy unit. All hy-
drogen atoms, -CF3 unit and some benzene rings are omitted for
clarity.
(d)
The samples were further characterized by an ESI-TOF mass
spectrometer with an electrospray ionization source in positive
mode (Figure 3). Intense peak at m/z = 1420.83 in Figure 3a
corresponds to the molecular ion [Au9(BINAP)4] 3+. The ob-
served isotopic patterns of [Au9(BINAP)4Cl]2+ and
[Au9(BINAP)4CF3COO]2+ are in perfect agreement with the
simulated (Figure 3b), and CF3COO- counteranions could be
confirmed in negative mode (Figure S4). The mass spectrum of
Au10 shows two prominent peaks at m/z = 1542.8 and 2371.2,
corresponding to the molecular ion [Au10(BINAP)4(p-
CF3C6H4C≡C)]3+ and dicationic ion [Au10(BINAP)4(p-
CF3C6H4C≡C)(CF3COO)]2+ (Figure 3c and 3d), respectively.
The isotopic distribution patterns are in perfect agreement with
the simulated.
Figure 3. (a) Mass spectrum of the Au9 cluster. Inset: The meas-
ured (black trace) and simulated (red trace) isotopic patterns of
[Au9(BINAP)4]3+. (b) The measured (black trace) and simulated
(red trace) isotopic patterns of [Au9(BINAP)4(Cl)]2+ and
[Au9(BINAP)4 (CF3COO)]2+. (c) Mass spectrum of the Au10 cluster.
Inset: The measured (black trace) and simulated (red trace) isotopic
patterns of [Au10(BINAP)4(p-CF3C6H4C≡C)]3+. (d) The measured
(black trace) and simulated (red trace) isotopic patterns of
[Au10(BINAP)4(p-CF3C6H4C≡C)(CF3COO)]2+
.
As shown in Figure 4, both clusters in CH2Cl2 show one prom-
inent absorption band at 426 nm, and a broad band around 500
nm tailing to 626 nm. Au9 has a peak at 320 nm, while Au10
exhibits an absorption at 340 nm. And Au9 shows a shoulder
peak at 444 nm while Au10 displays a characteristic peak at 467
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nm attributed to the presence of the P^P-Au-C≡CR motif,
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which can be used to differentiate it from Au9. The molar ab-
sorption coefficient at 426 nm of Au9 were calculated to be 2.1
*104 L·mol⁻¹·cm⁻¹ and is approximately 1.5 times of that in
Au10. The absorptions with wavelength larger than 400 nm are
associated with the metal cluster cores, because the BINAP lig-
ands and Au(I) precursors [(BINAP)Au2]Cl2 show no absorp-
tion in the region of 350-700 nm (Figure S5). The thermal and
photo stability of Au9 and Au10 were monitored by UV-vis
spectroscopy. No decomposition was observed after Au9 and
Au10 had been stored under ambient light for one week in di-
chloromethane, which shows their excellent photo-stability
(Figure S6). A CH3CN solution of Au9 was kept at 20 ℃, 40 ℃,
60 ℃, 80 ℃ for 10 min, respectively, then its UV-vis spectra
were measured (Figure S7). No obvious changes of UV-vis ab-
sorption spectra were observed, which indicates that Au9 has
good thermal stability. However, it was observed that Au10 was
converted to Au9 at elevated temperature such as 40℃ (Figure
S7).
(c)
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Figure 5. (a) Schematic illustration of interconversion between
Au9 and Au10. Blue curve: binaphthy unit. Some benzene rings are
omitted for clarity. Response of UV-vis absorption spectra at room
temperature: (b) The conversion from [Au10(BINAP)4(p-
CF3C6H4C≡C)](CF3COO)3 to [Au9(BINAP)4] (CF3COO)3. (c) The
interconversion between [Au9(BINAP)4] (CF3COO)3 and
[Au10(BINAP)4(C6H11C≡C)](CF3COO)3 in dichloromethane.
The CD Spectrum and the anisotropy factors. The
chirality of Au9 and Au10 has been confirmed by CD spectros-
copy as shown in Figures 6 and 7. The CD curves of (R)-Au9
and (S)-Au9 are mirror images to each other, indicating they are
a pair of enantiomers (Figure 6a). (R)-Au10 and (S)-Au10 are in
a like manner (Figure 7a). The chirality of Au9 or Au10 depends
on the handness of BINAP, i.e. the chirality of BINAP is trans-
ferred to the nanoclusters. Consequently, CD signal enhance-
ment was observed as shown in Figure S9a. It is worth noting
that apart from the CD features of the ligands and BINA-
PAu2Cl2, the CD spectra of gold clustersexhibit new features in
the visible wavelength region, similar to the previous observa-
tion by Schaaff et al.28 We ascribe the optical activity in the vis-
ible region to ligand-to-metal charge transfer (LMCT) because
the ligands themselves do not show optical activity in the visi-
ble region. The anisotropy factors of (R)-Au9/(S)-Au9 and (R)-
Au10/(S)-Au10 in the 250-350 nm range are very low (Figure
S9b), suggesting that π-π* transitions of (R)- and (S)- BINAP
contribute little to the optical activity of gold clusters. But pre-
vious studies by Tsukuda et al. revealed that enhancement of
the optical activity of gold clusters may be caused by diffusion
of π-electron of binaphthalene unit in vicinity to the Au core.15
The CD spectra of (S)-Au10(BINAP)4(C6H11C≡C) (black trace)
and (S)-Au10(BINAP)4(p-CF3C6H4C≡C) are almost identical to
each other, which indicates that the types of alkynyl ligands
affect slightly the chiroptical signals (Figure S10).
The CD spectra of Au9 and Au10 share a minimum at 568 nm
and a maximum at 342 nm as well as less intense signals at 380
nm, while some differences are evident. A shoulder at 363 nm
was observed with Au9 (Figure 8a) but not in Au10. (R)-Au10
has a negative peak at 265 nm and a strong and broad positive
peak at 467 nm (Figure 7a), while the negative peak of (R)-Au9
complex occurs at about 310 nm and the broad positive peak is
positioned at 426 nm (Figure 6a). The two systems both exhibit
intense and mirror-image Cotton effects in their CD spectra and
the peaks of their CD spectra are much more distinct than those
of the optical absorption spectra. The presence of P^P-Au-
Figure 4. UV-vis absorption spectrum of Au9 (black), Au10 (red).
Inset: Photographs of cluster Au9 and Au10 in dichloromethane.
The Reversible Interconversion. It was found that Au9
and Au10 could be interconverted (Figure 5a). The interconver-
sion is associated with the addition or removal of a RC≡CAu
component. As shown in Figure 5 b, after the addition of equiv-
alent amount of BINAP to the CH2Cl2 solution of Au10, the ab-
sorption at 467 nm decreases and the absorption at 426 nm in-
creases, which is indicative of that Au10 is converted to Au9. In-
terestingly, Au10 can be recovered by adding RC≡CAu to the
solution of Au9. C6H11C≡CAu was used in the conversion, be-
cause its good solubility is helpful for monitoring with UV-vis
spectroscopy (Figure 5 c). This Au10 can be converted reversi-
bly to Au9 again by adding BINAP to strip off the C6H11C≡CAu
component. The interconversion process was completed in
about 30 min, and the transformation was confirmed by mass
spectrometry (Figure S8).
(a)
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C≡CR staple has both a structural and electronic impact on the
(b)
(a)
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system. The interconversion between Au9 and Au10 was also
monitored by CD spectroscopy (Figure S11), which shows a
trend similar to that of UV-vis absorption (Figure 5b and 5c).
The intensity of CD spectra should be correlated with the
concentration of the sample, while the anisotropy factors is con-
centration-independent and g =Δε/ε =ΔA/A = θ [mdeg] / (32980
× A) (Δε: the molar circular dichroism; ε: the molar absorption
coefficient) were calculated in the wavelength range of 250-620
nm (Figure 7). The maximum anisotropy factor (gmax) of Au10
is up to 6.6 * 10-3 at 473 nm and is around 7 times higher than
that at 267 nm (Figure 7b). To the best of our knowledge, this
is the highest maximum anisotropy factor of gold nanoclusters
reported so far (Table S1). Similar to the trend in anisotropy
factors, the value around 450 nm of Au9 is calculated 3.7 * 10-
3, which is much higher than that around 317 nm (Figure 6b).
The result indicates that ligand-to-metal charge transfer (LMCT)
may play a key role in optical activity, whereas the contribution
of π-π* transitions of the ligands to the chiroptical properties is
relatively small. Notably, the highest anisotropy factors of Au10
is almost two times of that in Au9 (Figure 8b). The formation of
P^P-Au-C≡CR staple has influences on both the geometric and
electronic structures, which led to the enhancement of the g
value.
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Figure 8. (a) Comparison of the CD signal of (R)-Au9 (black trace),
(R)-Au10 (red trace) in dichloromethane (y-axis (θ) is in units of
mdeg). For CD analysis, samples were diluted to 1.3 × 10−5
mmol/mL. (b) Comparison of the anisotropy factor of (R)-Au9
(black trace), (R)-Au10 (red trace).
Computational Results. The correlation between the op-
tical activity and geometrical structure of the two clusters was
studied by DFT calculations. Cluster Au9 and Au10 are ideal
models for studying the origin of chiroptical properties of
nanoclusters because of the comparability between the two
well-defined structures.
As shown in Figure 9a, the calculated electronic absorption
spectrum of Au10 is in good agreement with the experimental.
The peaks at 573 nm, 467 nm, 426 nm and 340 nm, are well
reproduced. Simulated CD spectra of (R)-Au10/(S)-Au10 are
also presented in Figure 9b. One can see that Au10 exhibits five
peaks distinct from 250 nm to 600 nm, which closely match ex-
periment. As shown in Figure S12a, the first calculated CD
band 1 at 508 nm of (R)-Au10/(S)-Au10 correspond to shoulder
(b)
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peak I in the theoretical absorption spectrum at 502 nm (λexp
=
573 nm), which arises primarily from the HOMO→LUMO
transition (Table S2). According to the frontier molecular or-
bital diagrams (Figure S13), the HOMO is located over BINAP,
while the LUMO is on the metal core. The second CD peak at
450 nm is related to the absorption peak II at 450 nm, which is
ascribed to HOMO-2→LUMO, HOMO-2→LUMO+1 and
HOMO-4→LUMO transitions. Notably, the HOMO-2 is
mostly contributed by the P^P-Au-C≡CR motif (Table S3).
Therefore, the introduction of alkynyl ligands is crucial for the
CD band at 450nm (λexp = 467 nm). Moreover, the CD band 3
at 426 nm matches the absorption peak III (λexp= 426 nm),
which corresponds to the deep occupied orbitals to
LUMO/LUMO+1 transitions.
We also calculated the UV−Vis and CD spectra of (R)-
Au9/(S)-Au9 (Figure S12b, S14). We found that a weak CD
peak at 521 nm is related to the absorption peak I (λexp = 553
nm), and an indistinctive CD peak at 462 nm can be associated
with absorption shoulder peak II (λexp = 444 nm). These two ab-
sorption bands arise primarily from HOMO→LUMO transi-
tion and HOMO→LUMO+2 transition, respectively. Despite a
blue-shift, a primary absorption band at 426 nm from the exper-
iment is well reproduced in the simulated spectrum (Figure
S14). This absorption peak accounts for the CD band III (Figure
S12b), which mainly represents HOMO-9→LUMO transition.
It is worth noting that the absorption peak at 426 nm is related
to the transition of the phosphine ligand to the metal core, sim-
ilar to that of the Au10. However, there is no “P^P-Au-C≡CR”
motif in cluster Au9, so the absorption peak at 467 nm is miss-
ing. Consequently, the theoretical calculations confirm that the
optical properties in the visible spectral region are dominated
by electronic transitions from the ligands to the chiral core.
Figure 6. (a) The CD spectra of enantiomers (R)-Au9 (black trace),
(S)-Au9 (red trace) (y-axis (θ) is in units of mdeg). And UV−vis
spectrum of (R)-Au9 (dotted line) in dichloromethane. For CD
analysis, samples were diluted to 1.3 × 10−5 mmol/mL. (b) Corre-
sponding anisotropy factors of (R)-Au9/(S)-Au9.
(b)
(a)
Figure 7. (a) The CD spectra of enantiomers (R)-Au10 (black trace),
(S)-Au10 (red trace) (y-axis (θ) is in units of mdeg). And UV−vis
spectrum of (R)-Au10 (dotted line) in dichloromethane. For CD
analysis, the solution was diluted to 1.3 × 10−5 mmol/mL. (b) Cor-
responding anisotropy factors of (R)-Au10/(S)-Au10.
(a)
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Figure 9. (a) Experimental (black) and calculated (red) UV-vis ab-
sorption spectrum of Au10. (b) Experimental (solid line) and cal-
culated (dotted line) CD spectrum of (R)-Au10/(S)-Au10.
9
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CONCLUSION
We explore a facile synthetic strategy of homoleptic phosphine-
protected or mixed ligand-stabilized chiral nanoclusters. The
CD spectra give perfect mirror images and the identified peaks
of the experimental spectra are in good agreement with those
computed for the spectral range from 250 to 600 nm. The P^P-
Au-C≡CR staple in Au10 not only causes the reduction of chiral
symmetry from C2 to C1, but also has a strong effect on elec-
tronic system. These results reveal that using mixed ligands
may be an effective strategy to lower symmetry of chiral
nanoclusters. Intriguingly, we can realize reversible intercon-
version between Au9 and Au10 by the addition of BINAP or
RC≡CAu. Furthermore, insights from the tunable chiroptical
activity could provide a new platform to control the chiro-opti-
cal properties of metal nanoclusters and find their potential ap-
plications in chiroptical functional materials. Rational design of
ligand shell structures may be an effective way for controlling
the optical response of chiral nanostructures and aiding in the
research of reconfigurable switching of nanomaterials.
ASSOCIATED CONTENT
Supporting Information.
The Supporting Information is available free of charge on the
ACS Publications website at DOI:
Physical measurements and computational details, synthe-
sis and characterization data (PDF)
Detailed crystallographic structure and data for (R)-Au9, (S)-
Au9, (R)-Au10 and (S)-Au10 (CIF).
AUTHOR INFORMATION
Corresponding Author
*qmwang@tsinghua.edu.cn；*yangyang@jsnu.edu.cn
ORCID
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We thank Prof. D.-S. Liu and Center of Basic Molecular Science
for the help with CD measurements. This work was supported by
the National Natural Science Foundation of China (21631007,
21473139 and 21701064).
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G.; Jin, R. Chiral Ag23 nanocluster with open shell electronic structure
and helical face-centered cubic framework. Nat. Commun. 2018, 9
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c = 92.8172(14) Å, α = 90.00, β = 90.00, γ = 120.00°, V = 30167.3(8)
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30.3366(4) Å, α = 90.00, β = 98.232(1), γ = 90.00°, V = 18451.8(4) Å3,
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unique (Rint = 0.0840), final R1 = 0.0976, wR2 = 0.2581 for 59231 ob-
served reflections [I > 2σ(I)]. Flack factor = 0.013(5). (b) Crystal data
for (S)-Au9: a = 17.4001(3), b = 35.5243(5), c = 30.5610(6) Å, α =
90.00, β = 98.414(2), γ = 90.00°, V = 18687.2(6) Å3, space group P21,
7
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