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Structures and chiroptical properties of the
BINAS-monosubstituted Au38(SCH3)24 cluster†
Bertha Molina,a Ariadna Sánchez-Castillo,b Stefan Knoppe,c Ignacio L. Garzón,d
Thomas Bürgie and Alfredo Tlahuice-Flores*f
The structure and optical properties of a set of R-1,10 -binaphthyl-2,20 -dithiol (R-BINAS) monosubstituted AAu38(SCH3)24 clusters are studied by means of time dependent density functional theory (TD-DFT). While it
was proposed earlier that BINAS selectively binds to monomer motifs (SR-Au-SR) covering the Au23 core,
Received 3rd July 2013
Accepted 9th September 2013
our calculations suggest a binding mode that bridges two dimer (SR-Au-SR-Au-RS) motifs. The more
stable isomers show a negligible distortion induced by BINAS adsorption on the Au38(SCH3)24 cluster
which is reflected by similar optical and Circular Dichroism (CD) spectra to those found for the parent
DOI: 10.1039/c3nr03403h
cluster. The results furthermore show that BINAS adsorption does not enhance the CD signals of the
www.rsc.org/nanoscale
Au38(SCH3)24 cluster.
In recent years, interest in thiolate-protected gold clusters has
grown since the rst report of optical and chiroptical properties
of glutathionate-protected gold clusters by Whetten et al.
nding strong optical activity.1 Due to lack of structural information at that time the origin of optical activity could not be
determined (except for the fact that a chiral ligand is used for
protection of the cluster), although several mechanisms were
proposed.1,2 Nowadays, several structures of thiolate-protected
gold clusters are available.3 For example the Au102(SR)44 and
Au38(SR)24 clusters show intrinsic chirality of their Au–S
framework whereas the latter is achiral for the thiolateprotected Au25 cluster.4–6 Moreover, it was established that
Au38(SR)24 and Au40(SR)24 clusters show strong circular
dichroism signals even if covered by achiral thiols7 whereas the
anionic Au25(SR)18 cluster shows rather weak optical activity
when covered by chiral thiols (and no optical activity when
a
Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal
70-646, 04510 México D.F., Mexico
b
Escuela Superior de Apan, Universidad Autónoma del Estado de Hidalgo, Chimalpa
Tlalayote, Municipio de Apan, Hidalgo, Mexico
c
Molecular Imaging and Photonics, KU Leuven, Celestijnenlaan 200D, 3001 Heverlee,
Belgium
d
Instituto de Fı́sica, Universidad Nacional Autónoma de México, Apartado Postal 20364, 01000 México D. F., Mexico
e
Département de Chimie Physique, Université de Genève, 30 Quai Ernest-Ansermet,
1211 Genève 4, Switzerland
f
Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA
Circle, San Antonio, TX, 78249, USA. E-mail: tlahuicef@gmail.com
† Electronic supplementary information (ESI) available: Comparison of calculated
and experimental optical absorption and CD spectra of the A-38 enantiomer; bond
distribution of the A-38 enantiomer, and four studied regioisomers; tables with
the excitation energies, oscillator strengths and weights of the electronic
transitions; xyz relaxed coordinates of studied regioisomers, frontier orbitals of
the relaxed structures. See DOI: 10.1039/c3nr03403h
10956 | Nanoscale, 2013, 5, 10956–10962
covered by achiral thiols).1a,8–10 Taking into account the different
symmetry of the two cluster Au–S frameworks (D3 for the
Au38(SR)24 cluster5 and Ci for the Au25(SR)18 cluster4,11) one can
conclude that the more intense optical activity observed in the
thiolate-protected Au38 cluster is related to its intrinsically chiral
structure. In the Au25(SR)18 cluster,3b,13 the observed optical
activity in the presence of a chiral thiol is thought to be induced
by a chiral distortion of the initially achiral structure by chiral
thiols such as glutathione, while the phenylethanethiolate
(SCH2CH2Ph) ligand gives a null CD signal.4,11,14 Conversely, in
the case of much smaller chiral Aun(SR)m, (n ¼ 12–15, 16–20; m ¼
9–12, 12–16) clusters, the whole cluster structure (core and
ligand shell) is responsible of the intense CD signals.6
Our knowledge of the structure of the Au–S interface is based
on the X-ray crystallography of the Au102(SR)44 cluster showing
that the S and Au atoms form staple motifs which are bound to an
Au79 core.3a These motifs have been obtained from theoretical
calculations,12a and were systematically studied.12b The S atoms
become stereogenic centers upon adsorption of the ligands
(achiral). In addition the staples form a chiral pattern on the
cluster surface. In a similar way, the Au38(SR)24 cluster consists
of three SR-Au-RS (short or monomer) and six SR-Au-SR-Au-RS
(long or dimer) motifs covering a face-fused biicosahedral Au23
core (Fig. 1).5,9,15 The six dimer motifs form a staggered
arrangement at the endings of the prolate Au23 core while the
three monomer motifs are located at its equator.3d,5
Ligand exchange reactions, pioneered by Murray and
coworkers, are a useful method to post-synthetically alter the
properties of monolayer-protected gold clusters by introducing
new functionalities.16 Recently, Wang and co-workers reported
the synthesis of a novel thiolate-protected gold cluster with
outstanding stability, optical and electrical properties in which
compositionally both di-thiolates and mono-thiolates are present
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Fig. 1 Structure of the left-handed A-38 enantiomer. The Au, S, C, and H atoms
are yellow, red, gray and white, respectively.
in the protective monolayer.16e,16f The Au–thiolate bonding interactions were investigated by the early-stage reactions at the core–
ligand interfaces between the thiolate ligands and excess thiols,
through which the dithiols were found to replace monothiolate
ligands at 1 : 2 stoichiometry ratio, while addition of monothiols
into dithiolate monolayer instead of exchange was observed.
Assuming conservation of the cluster size, monodentate thiolates
are expected to bind to the adsorption site of the leaving thiolate.17 The situation is complicated and the possible adsorption
sites may be a consequence of the structure of the di-thiolate, as
its conformational exibility and the distance of the thiolate
groups have to be taken into account. For instance, decomposition of Au25(SR)18 clusters was thought to occur, but a recent
assignment of the reaction products shows that the cluster in fact
survives the exchange with BINAS (Fig. 2).18 Other place exchange
reactions with di-thiolate ligands were performed on the thiolateprotected Au25 cluster, showing conservation of the cluster
Fig. 2 The A-38 enantiomer, viewed along its C3 axis (upper left) and side view
(upper right). The six dimer motifs rotate anticlockwise i.e. following 1, 2 and 3
labels. Au atoms are in yellow. S atoms in red and blue colors are forming part of
dimer motifs while S atoms in green belong to monomer motifs. Structure of 2phenylethylthiol (2-PET) and R-1,10 -binapthyl-2,20 -dithiol (R-BINAS) are depicted
in gray (C atom), white (H atom), and red (S atom) colors.
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Nanoscale
size.19,20 As yet, little effort was put into the study of the binding
mode of di-thiolates. Noteworthy, Dass and co-workers studied
the Au25(2-PET)16(1,5-pentanedithiolate)1 cluster using density
functional theory (DFT). Bridging between two protecting units
was found to be the most stable conguration (interstaple
binding).20 Given the high conformational exibility of 1,u-alkane
di-thiolate, it is unknown whether or not the proposed binding
motif can be transferred to other kinds of di-thiolates.
Recent ligand exchange reactions between the intrinsically
chiral Au38(2-PET)24 cluster and bidentate BINAS indicated a
selective binding of BINAS to the short (or monomeric) staples,
SR-Au-SR.9,21 Specically, it was found by mass spectrometry that
only up to three BINAS ligands can replace up to six 2-PET ligands
even at longer exchange times. Because the known Au38 cluster
contains three short staples, it was argued that ligand exchange
of BINAS may take place selectively at the short staples.21a Later it
was found that the ligand exchange rate for the second exchange
is much slower than for the rst one.21b Therefore the observed
limited exchange could simply be due to kinetic reasons. In order
to shine light on these issues the present study aims at elucidating the stability of BINAS at different binding sites on the
cluster (inter- vs. intrastaple binding). We herein report a
computational study of the structure, optical and chiroptical
properties of derivative structures of the Au38(SR)24 cluster with
the general formula Au38(SCH3)22(BINAS)1. Methylthiolate was
chosen as model for the 2-phenylethylthiolate ligand. Motivated
by the observed preference of the le-handed enantiomer of the
thiolate-protected Au38 cluster for a BINAS with a R handedness
in ligand exchange experiments,21,22 an initial set of four isomers
with the anticlockwise enantiomer of Au38(SCH3)24 (A-38) and
R-BINAS was considered, which differ in the adsorption site of
the BINAS. Structural optimizations of Au38(SCH3)22(BINAS)1
regioisomers were performed without symmetry restrictions and
their energies and optical absorption and CD spectra were
calculated by using the ADF package.23 Indeed, a good match for
interstaple binding was found, giving rise to revision of the
previous explanation for the limited exchange. This study also
reveals a negligible inuence of the adsorbed BINAS molecule on
the chiroptical properties of the thiolate-protected Au38 cluster.
All DFT-GGA calculations were carried out using the PBE functional for the exchange and correlation (XC) terms, the Slater type
basis sets employed in the geometry optimizations are of polarized triple (TZP) quality with a [1s2–4f14] frozen core for Au, a [1s2–
2p6] frozen core for S, and a [1s2] frozen core for C. The energy
convergence criterion is tightened to 104 Hartree, and the
gradient convergence criterion is tightened to 103 Hartree per Å.
Moreover, ADF includes scalar relativistic effects through the
Zeroth Order Regular Approximation (ZORA).24 Time-dependent
DFT, as implemented in ADF, was utilized for the study of the
optical and chiroptical properties, through the calculation of its
excitation energies, and oscillator and rotatory strengths.25 To
calculate the optical absorption and circular dichroism spectra,
particularly in the low energy region (0.5–2.5 eV), the lowest 200
excited (singlet) states were considered, using the same XC
functional and basis set as for the structural calculations. To test
the reliability of the present TD-DFT methodology, a comparison
between calculated optical absorption and CD spectra of the
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Au38(SCH3)24 cluster with experimental data was performed,
indicating a good agreement, as it is shown in the ESI section
(Fig. S1†). Relaxed atomic coordinates for all regioisomers are
provided in the ESI† section also.
Initial Cartesian coordinates of enantiomers of the pure
Au38(SR)24 cluster were extracted from the available crystal
structure.3d In order to label the two enantiomers in the unit
cell of the Au38(SCH3)24 cluster we have orientated each
enantiomer along their C3 axis and observed the arrangement
of their dimer motifs. For example, Fig. 2 shows an anticlockwise rotation of dimer motifs of the A-38 enantiomer. The
assignment of the handedness of the cluster was recently done
by a comparison between measured and calculated CD spectra.5,7a The regioisomers considered here maintain both the
handedness of BINAS and of the thiolate-protected Au38
cluster but they differ in the position of BINAS ligand. Fig. 3
shows the optimized regioisomers where I1 shows R-BINAS
linked between two vicinal dimer motifs, I2 holds R-BINAS
adsorbed between vicinal monomer and dimer motifs, I3 has
R-BINAS linked to one monomer motif, and in I4 R-BINAS is
linked to one dimer motif. By comparison of the relative
energies of the optimized structures (Table 1), it emerges that
more stable regioisomers correspond to R-BINAS bound
between two gold adatoms located at vicinal staple motifs
(interstaple mode). The energy difference between I1 and I2 is
of 0.44 eV, and both regioisomers have R-BINAS linked in an
interstaple mode being favoured over the regioisomer with
R-BINAS bound to one motif only (intrastaple binding mode,
I3 and I4).
In a previous study of the Au25(SCH3)16(1,5-pentanedithiolate)1 cluster,20 the interstaple binding mode was found to be
energetically favored over intrastaple binding. Here, we have
calculated an energy difference of 1.05 eV between R-BINAS
linked to gold adatoms of vicinal dimer motifs (I1) and R-BINAS
linked to one dimer motif (I4). The calculated trend of R-BINAS to
link in an interstaple mode is in contrast to what has been
proposed in the past based on the number of exchanged BINAS
molecules in ligand exchange experiments.21a Since the preferred
binding site for the BINAS ligand is found to be an interstaple
motif between dimeric staples (I1), the initially proposed selective
binding to monomeric staples may not hold true.21b,22 Instead, it
seems likely that the limited exchange is due to kinetic reasons,
since it was found that the reaction drastically slows down aer
the rst exchange step.21b
The structure of the optimized pure A-38 enantiomer is built
by 72C–H, 24C–S, 48S–Au, and 104Au–Au bonds. Au–Au bonds
are included in the range 2.83–3.27 Å. Au–Au bonds forming the
Au23 core (Au(core)–Au(core)) are distributed in the following
manner: 12 bonds that involve two center Au atoms bound to
the Au21 shell; 57 bonds forming the Au21 shell and three bonds
between Au atoms that represent the icosahedral face-fused. I1
and I2 regioisomers show bond distances comparable to the
original A-38 cluster (see Fig. S2† for comparison) which can be
interpreted as a slight or null distortion induced by R-BINAS
adsorption. The negligible distortion may be due to a similar
S–S distance on R-BINAS before and aer its adsorption to Au
adatoms in staple motifs.
10958 | Nanoscale, 2013, 5, 10956–10962
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Fig. 3 Four optimized regioisomers (left) and a view of their local bonding
(right). (a) I1, (b) I2, (c) I3, and (d) I4 isomers. S, C, H, and Au atoms are in red, gray,
white, and yellow, respectively.
Bond length analysis of the optimized I3 regioisomer shows
that bonds between the two central atoms of the Au13 units
and their respective Au12 shells have an average bond length
of 2.87 Å, whereas all missing Au–Au bonds are in the range
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Table 1 D3 tolerance (D3), relative total energy (Erel), and HOMO–LUMO (HL)
gap of studied regioisomers
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I1
I2
I3
I4
Description
D3 (Å)
Erel, eV
HL, eV
R-BINAS/2 dimer motifs
R-BINAS/1 monomer and
1 dimer motif
R-BINAS/1 monomer motif
R-BINAS/1 dimer motif
0.10
0.15
0.00
0.44
0.91
0.89
0.25
0.28
0.88
1.05
0.63
0.53
The experimental absorption spectrum of the pure
Au38(SCH2CH2Ph)24 cluster displays two characteristic
signatures related to an electronic transition located at
1.99 eV, and a less dened peak located at 1.64 eV.29 Calculated optical absorption of the A-38 enantiomer (Fig. 5) shows
two peaks located at 1.99 and 1.66 eV in good agreement with
experimental results as can be seen on the line-shape
obtained through the broadening of the associated oscillator
strengths (f) represented as colored sticks. Fig. 5 shows
optical absorption spectra of A-38 and all four studied
regioisomers.
2.80–3.29 Å. The Au–S bonds between Au(core) and S atoms
forming the monomer motifs are around 2.44 Å, and bonds
between Au(core) and S atoms in the dimer motifs are circa
2.43 Å. Au–S bonds in the monomer and dimer motifs have an
average bond length of 2.35 Å. It was found that once R-BINAS
is bound to a monomer motif (I3), it induces a distortion
resulting in two Au–S bonds between 2.38 and 2.55 Å. The C–H
bonds of methyl and R-BINAS ligands are around 1.1 and 1.0 Å
respectively. Further structural analysis shows that all the
studied regioisomers hold an entire C1 symmetry (including
the ligand shell).
In order to study the distortion induced aer R-BINAS
adsorption, we analyzed isolated Au23 cores nding that the
pure A-38 cluster has a D3 symmetry when a tolerance of 0.09 Å
is applied. I1, I2 and I3 hold D3 symmetry with a tolerance of
0.10, 0.15 and 0.25 Å respectively. These results conrm that the
Au23 core of the A-38 cluster is intrinsically chiral with a slightly
larger distortion induced in I4 (0.28 Å) which can as well be
considered as an entire C1 structure (see discussion on Fig. S2†).
It is interesting to note that the distortion of the original A-38
core goes along with a destabilization of the corresponding
cluster (Fig. 4). A large relative energy was found for I4 (1.05 eV)
being the main reason to discard it in the present discussion.
In general, the electronic stability of the studied regioisomers
may be understood on the basis of a shell model, considering 14
delocalized valence electrons.26,27 In fact, the features of the
optical absorption spectra are related to the cluster geometry,
such that it can be used to distinguish between each other.5,13b,28
Fig. 4 Correlation between the Au23 core distortion, HL gap values, and relative
energy of studied regioisomers. The core distortion is given as the tolerance (Å)
necessary to obtain a D3 point group.
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Fig. 5 Calculated optical absorption spectra for the A-38 enantiomer and RBINAS substituted regioisomers. Some transitions are labeled as a, b and c in ESI.†
A Gaussian broadening of 0.1 eV has been used. With asterisks are identified on
A-38 spectrum two characteristic peaks along all calculated spectra.
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From the structural analysis mentioned above, I1 and I2
regioisomers have a similar Au23 core which might result in
similar optical absorption spectra with respect to the A-38 cluster.
This expected behaviour was conrmed by the calculated spectra
shown in Fig. 5. In I2, a slightly more intense peak located at
1.65 eV was found, while I1 shows an intense peak located at
2.0 eV. However, the changes for I3 and I4 regioisomers with
respect to the parent A-38 cluster are more pronounced with
peaks located below 1.0 eV. Those electronic transitions under
1.0 eV, are related to weak HOMO1 to LUMO and HOMO–
LUMO electronic transitions as it will be shown later.
The A-38 optical spectrum shows a HOMO1 to LUMO
transition, located at 1.06 eV, while the I3 regioisomer shows an
intense peak located at 0.98 eV attributed to HOMO1 to
LUMO+2 transition. In addition, I3 has one weak signal located
around 0.69 eV related to a direct HOMO to LUMO transition.
This peak under 1.0 eV was found more intense in I4. Aer a
Kohn–Sham orbitals analysis of the four studied clusters, it was
determined that the HOMO level is located at similar energies,
but the LUMO level suffers an evident shi toward negative
energies for I3 and I4 regioisomers (Fig. S3–S7†). The shi of the
LUMO level of I3 and I4, has an effect in the character of the
Kohn–Sham orbitals, in such a manner that the frontier orbitals
of I3 and I4, exhibit a major character of ligand-based orbitals
(Fig. S6 and S7†). In general, in thiolate-protected gold clusters,
electronic transitions located under 1.0 eV are not expected to
involve electronic levels with ligand character because the HL
transition is characteristic of core transitions (ngerprinting).
The mixing of ligand character into the frontier orbitals in I3
and I4 is therefore considered as further support to explain their
higher relative energies.
In the case of I1, one peak located at 1.03 eV represents a
HOMO to LUMO+1, and HOMO1 to LUMO transitions. In I2
regioisomer one peak located at 1.04 eV is yielded by HOMO1
to LUMO+1 and HOMO1 to LUMO transitions.
Another peak located at 1.36 eV in A-38 is present at 1.30 eV
in I3 with an enhanced oscillator strength value. At 1.47 eV is
located a peak that does not have a counterpart in the A-38
spectrum. Two peaks in I3 coincide in their position with the A38 spectrum (1.6 and 1.78 eV). In general two peaks located
around 1.64 eV and 1.99 eV in A-38 can be considered characteristic along all calculated regioisomers. Further differences
were found for I3 regioisomer which shows a peak around 1.25
eV with major intensity. Both strongly distorted regioisomers I3
and I4 show a largely reduced HL gap (Table 1) and transitions
far below 1.0 eV, both in optical and CD spectra (Fig. 5 and 6).
Before CD spectra discussion, it is important to recall that I3
was found more distorted aer BINAS adsorption and its
absorption spectrum shown in Fig. 5, consistently shows less
structure. This result points to a relation between lower
symmetry of the core and a less structured absorption spectrum
in I3. Furthermore, it is evident that the absorption spectrum
does not change much for isomers I1 and I2, compared to the
parent cluster, whereas for I3 (and I4) the spectra change
drastically. Experimentally, it was found that one BINAS ligand
has only a minor effect on the absorption spectrum,22 which is a
further argument for interstaple binding.
10960 | Nanoscale, 2013, 5, 10956–10962
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Fig. 6 Circular dichroism spectra for the calculated A-38 enantiomer and R-BINAS
substituted regioisomers. A Gaussian broadening of 0.1 eV has been used.
The CD spectrum of the Au38(SCH2CH2Ph)24 cluster were
measured aer enantioseparation and the following position
and phase of the peaks were found (see Fig. S1†):7a 2.82(+),
2.59(), 2.2(+), 1.97(), 1.66(+) eV. The calculated CD spectrum
of le handed enantiomer of Au38 (A-38) protected with methyl
ligands has the coincident peaks: 2.57(+), 2.19(), 1.93(), and
1.64(+) eV and we calculated additional peaks which are not
reported in the experiment at 1.35(), 1.14(), and 1.03(+) eV.
Regarding the calculated CD intensities (rotatory strengths),
they are similar for peaks located at 1.93 and 1.64 eV.
Due to the fact that CD spectra are more sensitive to the
structure, calculated spectra show large differences between the
regioisomers. First of all, I3 and I4 show peaks located below
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1.0 eV which are not present in the pure A-38 structure. One
negative peak located at 1.93 eV in A-38 and two positive peaks
located at approximately 1.64 and 2.42 eV are less intense in
substituted R-BINAS isomers. It appears that adsorption of
R-BINAS on the chiral Au38(SCH3)24 cluster does not enhance
the CD signals. This is supported by experimental ndings. For
I3 even considerable less intense signals were found. Of note,
calculated CD spectra of I3 and I4 are the weakest of all
considered structures although their Au23 cores are most distorted. The structural analysis let us correlate weaker CD signals
to more distorted Au23 cores for all R-BINAS-substituted
regioisomers. However this assertion needs to be taken with
reserve because CD signals arise not only from the Au23 core but
from the whole structure.
As is evident from Fig. 6 the calculated CD spectra of I1 and
I2 are similar to the spectrum of A-38 in the range 1.0–2.5 eV.
It is important to notice that experimental circular dichroism
curves where obtained from 1.5 to 4.5 eV.22 However, given the
complexity of the present calculations (mostly because of the
high use of memory), theoretical curves span the range from
0.5 to 2.5 eV. In other words, comparison of experimental and
theoretical curves is limited to the spectral region comprises
between 1.5 and 2.5 eV.
Fig. 7a depicts the experimental curve of A-Au38(SCH2CH2Ph)22(R-BINAS)1 against the calculated CD of the I1
regioisomer. The experimental and calculated spectra of I1 agree
on at least three peaks (position and sign); two positive peaks
located around 1.68 and 2.45 eV, and one negative peak located
around 1.97 eV which relative intensity is reproduced, while one
positive peak located around 2.18 eV was found less intense and
with opposite sign in the calculated I1 spectrum. The calculated
negative peak located above 2.5 eV must be considered as not
characteristic because it is on the limit of the calculated range
and it might be necessary to extend that range to get a more
reliable sign for it.
In the case of I2 one negative peak located at 2.21 eV is less
intense and positive in the experimental spectrum and one
Nanoscale
negative experimental peak around 2.0 eV is located toward low
energy in the calculated one. As can be seen in Fig. 7b, position
and sign of peaks of I2 show less agreement with the experimental spectrum as compared to I1. Overall, the CD spectrum of
I1 is in best agreement with the experimental one.
Conclusions
In summary, structural, electronic, optical and chiroptical
properties of a set of A-Au38(SCH3)22(R-BINAS)1 regioisomers
having the same handedness of the Au38(SCH3)24 cluster and
BINAS but differing in the position of BINAS adsorption were
analyzed using TD-DFT. It was found that R-BINAS prefers to
bind between two vicinal dimer motifs located at endings of the
prolate Au23 core. We have found that I1 and I2 regioisomers
maintain almost intact the Au23 core of the Au38(SCH3)24 cluster
aer R-BINAS adsorption, whereas considerable distortion was
found for the other adsorption sites. A-38, I1 and I2 show
similar optical absorption and CD spectra, which is consistent
with experimental ndings. Furthermore, there is no evidence
that adsorption of chiral R-BINAS enhances CD signals. An even
less intense CD spectrum was found for the I3 isomer, which
shows a strong distortion in the Au23 core. The calculations also
show that the CD intensity is not only related to a more or less
distorted gold core but that the whole atomic structure of the
Au38(SCH3)22 (BINAS)1 cluster has to be considered.
Acknowledgements
B.M acknowledges support by PAPIIT-DGAPA, UNAM IN119811.
I.L.G. acknowledges support from Conacyt-Mexico Project
177981. S.K. and T.B. gratefully acknowledge nancial support
from the University of Geneva and the Swiss National Science
Foundation. S.K. is grateful to the German Academic Exchange
Service (DAAD) for a postdoctoral fellowship. A.T.-F. acknowledges to CONACYT and to the NSF for support with grants DMR1103730, “Alloys at the Nanoscale: The Case of Nanoparticles
Second Phase and PREM”: NSF PREM Grant # DMR 0934218;
“Oxide and Metal Nanoparticles – The Interface Between Life
Sciences and Physical Sciences”. We are grateful for the facilities of the Dirección General de Cómputo y de Tecnologı́as de
Información y Comunicación (DGTIC-UNAM) during the realization of all the calculations.
References
Fig. 7 Circular dichroism spectra of calculated (colored curves) and experimental
A-Au38(SCH2CH2Ph)22(R-BINAS)1. (a) Comparison of experimental with the
calculated curve of I1, (b) comparison of experimental with the calculated curve
of I2.
This journal is ª The Royal Society of Chemistry 2013
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